Please suggest bookshelf with best bass response under $4000 pr.

Lately, I've been craving deeper, tighter bass. I'd like to hear some ideas for replacing my Silverline 17.5 monitors. Is this a stupid question, due to inherent limitations of driver size imposed by typical bookshelf dimensions, or might I actually do better with another speaker? Amplification is Wells Audio 150 watt SS Majestic integrated. Source is aging Jolida JD100 tubed cdp (in new year, I plan to replace this with another SS cdp or a transport/standalone dac combo). Thanks ! 
I just found an a'gon ad for monitors with this claim: 

"The __________ are full range Studio Monitors that will
provide the entire frequency range, therefore, eliminating the need of using a subwoofer which cannot be fully integrate with speakers".

I wasn't aware such performance was even possible. Any thoughts ? ? ?  

Neat isobaric (Momentum, Ultimatum) bookshelf speakers have excellent bass for the size. Both can be found used for under 4k. ProAc Response floor standing models also have very solid bass and they sound great with the Wells Majestic. The footprint is no larger than a good bookshelf speaker stand. 
Theoretically a smaller driver with greater excursion can go deep but at the expense of sensitivity.  Ports or transmission line can extend frequency response down as well.  There's no substitute for a big driver in a big box, though.  In my experience you can never get the same visceral impact from small speakers, with or without a sub, that you can get from big ones.  If you're determined to try, the best way to go is active.  Active bass is better.  I consider an 8" driver to be the smallest driver that can begin to give a satisfying punch and go deep enough to not sound wimpy or low resolution on music with siginificant bass content.

Is there some reason you absolutely can't have floorstanders?  Small floorstanders with a pair of 7 or 8" woofers will have a far better chance of satisfying you than another bookshelf speaker.  If you've got your SIlverlines on stands the amount of floorspace taken up will be about the same.  

I'd check out the Dynaudio Confidence C1. I heard a pair once, and was absolutely astonished that so much deep, controlled bass could come from such a (relatively) small stand-mount.

The laws of physics remain what they are. You cannot get deep bass out of a small box and small drivers. The more you push low frequency extension, the higher the distortion. Of course technology marches on, but only slowly. In my own case, I recently replaced the LS3/5a monitors in my study by their most modern descendants, the Harbeth P3ESR. The modern sibling does indeed have more extended bass, and better bass as well (and not just bass - these are truly great speakers), but even so, it is nothing like a true full range speaker. Not in terms of low frequency extension, and not in terms of dynamic potential.
If you want deep bass there are only two possibilities. The first is new full range speakers. The second is subwoofers. As it so happenend I have a B&W PV1d subwoofer in my main system, and one day I decided to experiment and combine it with the little Harbeths. The match was easy to achieve and the sound was spectacularly unreal. You think all that deep bass is coming out of these two litle boxes. The extra power from the sub also gave some more dynamics, even though it still did not quite fill the large main listening room that I was using for the experiment.
So if you are happy with your current mini monitors, I think the subwoofer route is the way to go. If you decide to do this, I have two recommendations, and they both concern room modes. Room modes are the real problem of low frequency reproduction, and they have to be addressed if you want a good integration, and want to avoid boomy and woolly one tone bass. I think you would need to do two things. The first is to use multiple (small) subs - at least two and perhaps more, to smoothen response. See here for an introduction:
Have a look at the Audiokinesis Swarm system:
The second would be to add room equalization like the Antimode 8033: I have one and I am very pleased.
Combine multiple subs with room eq, and you have the best of what is possible in a domestic context.
However, if you are using mini monitors because your room is very small, forget about all this, and just learn to live with what you have. How large is your room?
I nominate williemj for post of the week...or maybe the month!  Nothing more to be said. 

The Totem Mani-2 used to have the most impressive bass I've heard out of a monitor-sized box.

None of their current stand-mount options are specified below 40 Hz.

I'll second Dynaudio for big punchy bass out of a small box. I'll also throw in the Guru QM10/2. Really fun and great voiced little speaker with lots of bass. Dynaudio will play louder. 

Proac's as someone mentioned already. 

 AudioNote AN speakers are all stand mounts and the AN-E's go very deep indeed (effective bandwidth from 18 Hz to 23 kHz at -6 dB) The smaller AN J's go to about 25hz If your patient you can get the AN-E Lux in your price range and the J's are new starting in your price range.

PMC have some very good small speakers with transmission lines that go fairly low as well.    

Disclaimer I am a dealer. I would strongly suggest you find a local dealer in addition to bryston mini T bottom end is unbelievable well under 4000 coherent transparent fantastic
Laws of Physics being what they are audition a REL subwofer that is within budget and size in your room and keep your monitors!
Look look for used Wilson Audio Duette speakers. Truly exceptional and tight bass.
The best bass I ever heard from a relatively small enclosure was the Totem Mani 2. There are two woofers in tandem, one is internally located in the cabinet behind the baffle mounted driver and helps push/pull it.

Why not a bookshelf like the Golden Ear AON 3 (well below your budget) ? I have heard other speakers from Golden Ear , and was highly impressed. These stand mounted speakers use the same excellent folded ribbon tweeter they use is their floor standers, and claim bass extension down to 38Hz.

Also, as others have posted, you might look for a pair of good, musical subs, like smaller RELs, Golden Ear subs, JL Audio subs, or a Vandersteen 2Wq (provided your Silverlines extend down to 40Hz, and your amp has a tape loop). You can keep your Silverlines, which probably have mids and highs as good as anything you can find within your budget,

I apologize for the late response. . . 

RE: recommendations for Dynaudio, the Silverlines use Dynaudiop drivers, for whatever that's worth. No doubt, there are other design variations that come into play from one box to another. 

RE: recommendations for sub(s): I've received very inconsistent advice from sub vendors re: subwoofer placement and because I don't have many potential places to locate a sub, I've avoided going down this road.

willemj: The room is about 15 X 20 and it adjoins a dining room separated by a wall that's about 5' tall (living room is "sunken") and an entry. Thanks for the detailed technical info re: subs. Unfortunately, as mentioned, I have little flexibility/space for subs and having to locate multiple subs simply isn't practical. 

Jon_5912: The choice of monitors rather than floor-standers was my response to inability to move furniture that would obstruct floorstanders.
Unfortunately, I do not enjoy the luxury of a dedicated listening room in my present house. Hopefully, I will in the next one! 

Thanks to all who've suggested other monitors to try.

Meadowman: Yes; I am aware of the Mini T's! They indeed look like a very promising solution but I fear WAF will be an issue. 
Not even one or two really small subs like REL T Zero or the slighter larger SVS SB1000? You can tuck them away in two corners of the room and equalize the boost from the room corner.
For me, the best small high quality speaker with quite decent low frequency extension would be the Harbeth M30.1, but I have obviously not heard all that is on the market. See:
willemj: In fact, the SVS is one I've definitely considered. But as I've said, when I ask salesmen about the fussiness of sub placement, they always hedge their responses, which makes me hesitate. I did read the Harbeth review. . . interesting! Will have to research whether any Northern CA audio dealers stock them. Thanks for the suggestion! 
I faced similar domestic restrictions and opted for a B&W PV1d to match our minimalist modern interior.
I think the concerns about placement and integration of subwoofers are to be taken seriously, but they can be overcome without too much difficulty. The problem is room modes, the resonances at critical dimensions of the room. With the traditional unequalized single (big) sub, finding the right spot and creating good integration is indeed hard. The solution is simple and twofold: multiple subs (two small ones is usually enough) and room equalization. Two small subs will smoothen the response because the peaks and dips from one sub’s location will not be at the same frequencies as from the other sub’s location. In practical terms, as the DSpeaker Antimode engineer told me, just push two little subs into two adjacent corners of the room, benefit from corner boost to get rid of dips/nulls, and use equalization to reduce the peaks. Using the very affordable DSpeaker Antimode 8033 is dead easy: it is automatic, and takes maybe half an hour, including reading the manual. The result is quite dramatic, changing bass response from woolly and ’slow’ to tight and ’fast’. The Antimode will also equalize the response of just one sub (as in my case) but only for a more restricted listening area. That area gets significantly larger with two. So next on my purchase list is a second PV1d, but that is another story.
I would think that in a medium size room like yours, two small subs in the room’s corners would be visually more attractive than, for example, larger floorstanders (that often also introduce bass response problems). As for SVS, they have a generous return policy, so you are not risking much. Listening to subs and comparing them in a dealer's demo room is next to meaningless, because you are listening to the character of the room rather than the sub.
I had an SVS subwoofer many years ago that needed service. SVS reps just blew me off, stated I needed to buy another sub. They would not look at my sub, and I bought it from them. That really turned me off to SVS. YMMV.

Who knows, I haven’t heard them all .
That said, my Totem Signature 1’s ,2200$ new, I paid 900$ for mine 3-4 years ago do not require a sub for the acoustic jazz and classical I listen to .
As most rock is engineered to have big bumps at 80 to 120 hz don’t see why they wouldn’t work there..
The Totems are solid and clear down to 50hz which is all that is required unless Bach organ pieces are your main listening fare . Even then clarity of the reproduction of the next octave above is all you need to be fully into the music .
I second PMC monitors - the newest twenty5.22 are really better than the older versions. Great sound staging and definition. Bass mass is not more than other monitors but they go lower and most important keep the PRAT (pace rhythm and timing)! If you want more bass mass try to get that with source and amplifier. Compared to monitors with 8" woofers (slower) the PMC´s are more satisfying. 
There is nothing slow about the 8" woofer in Audio Note AN-J's. ATC sealed bookshelf speakers with proper amplification have a certain speed to them I haven't heard in any ported design. For straight up bottom end go with Isobaric designs like Neat Momentum, Totem Mani-2, various Wilson Benesch etc...
I just got focus 160s. They’re discounting heavily now if you can find new at a dealer. 
Huge bass, incredible sound and imaging.
I've been through the speaker challenge for a small room. I chose the ATC SCM-19. You need some power, but they do very well in a small footprint. Excellent detail and speed. They are right at budget as well.
+1 on the Totem Mani 2 if it is bass you desire.  With your outstanding amplification, a pair of used Dynaudio C-1's or Joseph Audio Pulsar's will rock your world and you can forget about needing a subwoofer.  
Check out Legacy Studio's Studio HD's.  Strong bass down to 40Hz and a very good looking speaker that will blend in with your wife's room decor. I have compared the Studio's to Kef, Revel, and most other bookshelf speakers... At less than $2000 for a new pair in the Rosewood or Black Pearl finish they're hard to beat.
Acoustic Zen adagio junior or Bryston Mini T, They are substantial big for bookshelf speakers but will bring you deep strong bass  as stand floor speakers .
There are so many really amazing bookshelf speakers e.g. Kef, BW and so on.  I would try to listen to the newer Elac bookshelf speakers designed by Andrew Jones.  You could save the extra money for a subwoofer (again, so many great designs) to take care of those frequencies that you can really feel.  Again, check out Elacs sub offeringa as they are so cost-effective.
Lastly, matching your amp to the speakers is critical and there isn't a better method than listening to the setup.  If you can find the right dealer they will accommodate you.  When I purchased my last speakers I carried my (heavy) tube amp to two dealers who wired it up for me to really get the sound I was listening for.  Take your time...  and enjoy!
Bass response is so much more than the speakers themselves. Placement relative to listening position, and room relative to same are critical elements. Getting the bass "right" at the MLP, is in my opinion the most significant thing in this hobby. It is very much worth the effort to learn how to accomplish this.
To that end I'd be of them mind to add a sub with EQ to your existing setup. But really you should measure what's going on at your listening position so you know where to focus your attentions. A Umik1 & REW would get you there.. 
Others are right about the limitations of driver vs cabinet size etc.. but as mentioned above there are speakers like Golden Ear's Aon that use passive radiators to effectively increase cabinet size and bass response. 
One thing a lot of audiophiles either forget, or don't know is that as the frequencies get lower, our ability to hear distortion decreases proportionately and also we perceive them to be quieter relative to the rest of the spectrum. (Search Munson curve)
If a speaker like the Aon is rated +/- 3db from 38hz & up it doesn't mean there isn't effective bass below that frequency, and you could probably not physically hear between 5% to 10% distortion down there anyways. The room itself can create as much as 30db swings through the audible range and usually the biggest swings are in the bass frequencies. 
IMO getting the bass right creates the clean canvas for the rest of the spectrum to paint on. 
Dunaudio C1. Just wonderful. Used for $4 or less. Be aware there are a couple iterations. 

You really need to go and try to hear some of your possible contenders.

I think what many of the add a sub guys are failing to notice is your speakers look to be from 1998 if this is the case of course loudspeakers from today will offer more clarity.

The issue of bass is as much of how the room is interacting as well as the capabliities of the loudspeakers.

ATC makes screaming good monitors that are very neutral and throw a huge soundstage, they are also very dyanmic with good bass, hoever they are not that efficient, and like power, they also have very tight bass but it is not subwoofer quantity.

The Dynaudio C1 are very fine monitors they only go down to 45hz and are also power hungry. 

If you are really looking for subwoofer level bass out of a small speaker, we were exhibiting at the New York Audio Show with the Legacy Cablire which is a bit more than your budget, however, they had unbelievable bass which was tight and room filling, the 8 inch woofer has 1 inch of linear throw so it can move some air and the speaker has dual passives.

If you can squeeze up to $5500 you will be blown away be their performance and they are quite compact and stunning looking they are also efficient and play loud. The Calibre is flat down to 38hz which is very impressive for a monitor.

The Calibre’s also image extremely well and use a state of the art Heil AMT tweeter mated with a fantastic Italian midrange driver.

Dave owner
Audio Doctor NJ

If you can swing an extra $500, try a pair of Neumann KH310A monitors. They are small, they go low, and yes, I have a pair. You won't be disappointed.

Spenceroo, most people don't want a pair of hideous pro speakers in their Living Rooms, you mistake what sounds good and what most people want to have in their homes. 

A high performance speaker should fit nicely into someone's home and decor. 

OP you need to get yourself to some of your local dealers and or Audio shows and actually listen to some of the newer contenders in your price range.

I would put ATC, Legacy, on your list in the uber monitor range, If you really want deep bass very few speakers that are this compact hit as hard and go as low. 

The Wells amp is powerful enough to drive almost anything. 

Go forth and listen. 

Dave and Troy
Audio Doctor NJ
Well, if you check the OP's 2nd post, he mentions studio monitors, hence the suggestion. I don't see a problem myself. 
I second the nomination of the Elac Adante AS-61 monitors. The first shipment will be coming in sometime around 11/16-11/20 and every week thereafter. I, myself, am waiting to hear them as I liked the floor standers. 

They're a there way design with a sealed box, something that you don't see much of with monitors. They vent via the passive bass radiator on  the front (the actual bass driver is situated behind it). You'd save $1.5K and just may like it.

Another one would be the Studio Electric M4 for around the same price as the Elacs and they, too, are a sealed design. I've yet to hear them but the chatter is they are very good. I'm lucky in that I can listen to both in my area. Try to audition before you commit.

All the best,
You have some really nice monitors.  If u like the rest of their sound I'd highly recommend adding a sub with some integration hardware to help them blend.  Specifically, I'd get a used DSpeaker antimode 2.0 for about 500 bucks and an SVS SB1000 used for about $300 and see how that works out.  My bet is you'll be in music heaven (both available here now), but if not u can sell the sub and processor for little or no loss.  Short of going this route, I'd look for a used pair of Joseph Audio Pulsars, but I'd try the sub route first because you'll get the benefit of lower bass that can be so transformational to a system properly done.  Best of luck. 
Ive also heard great things about the Elac AS-61 monitors but they might just suck every amp of current from your amplifier in order to sound as they should.
The Calibre mentioned earlier is also very impressive both esthetically and sonically but they’ll push you way out of your budget when considering the cost of the stands required to match their quality.
Just as an aside, the monitors that keep blowing me away everyime I see/hear them at the NYC Audio Show are Sonner speakers designed and made in Massachusetts and only one model in their lineup. If you close your eyes you think they are huge floor-standers with incredible imaging and a wide and deep soundstage. Just boggles the mind how it could make this sound out of a two way pretty small monitors.The problem is they cost $10K and $12K including the stands. Probably others heard them as well at the show.
Yes, the Sooner monitors are absolutely killer. I fell quite hard for them when I first heard them but the $7K asking price gave me pause. They have some of the most beautiful, expressive, and airy highs I've heard. So much so that at first I thought the mids and bass were lacking a bit, but it was just that I was hearing, for the first time, some excellent rendering from the upper mids and highs. A great choice if you can afford them.

As for the power hungry Elacs (85db) I have no problem driving my 85db Clearwave Duet 6 monitors to lease breaking levels with my 90 watt Marantz integrated. 😃 That Well Audio integrated should be able to handle them.

All the best,
My harbeth c7es3 have great bass response.   Way better than the 30.1 imo.   Just a fantastic speaker all around!   Plus it matches up with most amps.  I do prefer a solid state preamp with them.  
I owned a couple pairs of Totem Mani-2’s and if you have enough power from a good SS amp, you will get very good bass. I had a 200 watt Classe CA-200 amp at the time and they needed more power. I teamed them up with the McIntosh 1000 watt monos and they sounded amazing. 
The Mani 2 is a stunning speaker but know you'll need a seriously beefy amp to feed it. If it doesn't double down from 8 -> 4 ohms don't bother. Rewarding at the end of the day though!!