advice on possible (REL?) sub for PSB Imagine B speakers

I know nothing about subwoofers! I have a couple specific questions and a couple general questions. Here goes.

The context: I recently said goodbye to my old Maggies (1.5), which I loved. I picked up a pair of PSB Imagine B speakers. I'm not sure they're a long term solution but, for a few reasons, I'd like to give them a run for a year or two. I like them! Still, I really miss the Magnepan sound; the fit, literally, just isn't right in my house. For that matter, a floor-standing speaker wouldn't be ideal. Big windows, big view--so perhaps not big speakers. (I love my wife!)

I'm wondering if a subwoofer would open up the sound of my speakers, give it more "air," more warmth and immediacy. I play primarily classical and rock; not surprisingly, it's the classical that I want to enhance. I don't care a whit about rattling windows or big booms. I want something that is "musical" and that gives more presence not only to the lows (organ, double bass) but to the mids (cello, bassoon). As is often said, I don't want to hear the subwoofer when I'm listening. Finally, I want more from these speakers now but I would also want a sub that could work with future speakers.

Almost everything I've read about REL sounds promising. I'm looking at the S3 SHO (still available with a little searching) or the S510. I did read something, somewhere, that the REL subs are designed to complement high-end speakers and not bookshelf speakers. So perhaps it wouldn't be a good fit? I'm open to other subs but REL seems to be saying the right things. Also, smaller is better, space-wise.

Here are my questions:

1) While I realize it might be odd to spend twice as much on a subwoofer (say $2000) as on speakers, is my approach otherwise nonsensical? Should I put to rest the subwoofer idea and save the money for better speakers down the road? Would a well-matched sub have the potential to open up my speakers now? (I do know that placement, etc, is crucial.)

2) More specifically, would the REL work well with the PSBs? Is there a reason they might not be a good fit for bookshelf speakers?

3) More specifically still, the speakers are ported--would I need to block those ports? 

Thank you all so much!

Hi northman,

I have the REL T7i with the Joseph Audio Pulsars.  Wonderful coupling.

1)  Makes perfect sense.

2)  Oh yes.  Once properly placed and adjusted, you'll be a very happy camper.

3)  No If placed and adjusted properly.

Other thoughts.  Depending on the size of your room,  you may not need the S3 or the 510.  A smaller model might be a better choice so you don't overload the room.  And buy from Amazon, Cruthchfield, or Music Direct.   Can return for full refund.

Good luck.   Your headed in the right direction.
Thank you, bubinga--that's an encouraging response! I was thinking about the S3 because it seems to be a bit smaller than the 510 ... but I'll keep thinking!
ps: I had to look up Joseph Audio Pulsars. Dang. "Bookshelf speakers" beyond my imagination!
Adding a Rel subwoofer (T/5i) to complement my Kef LS50s was the best decision I've ever made. It completely transformed the musical experience with increased scale and soundstage (width & depth) as well as added warmth. FWIW, the LS50s run full range with no bungs in the ports and I use the recommended High Level (Speakon) inputs on the Rel.  
Tonight is one of those nights. Almost feel like saying get the REL, its The Lord of the Subs, the One Sub to Rule Them All. Because, tired of explaining. But yet not feeling quite that sarcastic. On the fence. So do yourself a favor, type into the search bar, "Swarm subwoofer system" then search here for all posts by Audiokinesis and noble100, then search for "Earl Geddes subwoofer." Then if you still haven’t figured it out, make Sargon proud. Get the REL. It is a magical sub.

Seriously. Even better. REL is the Bose of subs.
Thank you all very much, including Gandalf. I'm now thinking about the T5i or T7i, but I'm still learning, obviously. I'm sure this question is addressed repeatedly out here and elsewhere but I'm going to expose my naiveté and ask it anyway. I understand the principle of matching the sub with the speakers, system, and room, but I don't entirely understand the application. Within reason, why wouldn't I want the best sub I can afford? Can't I just ... turn it down if it's too much for my room? Would a higher-end model (S/510, e.g.) be potentially more difficult to place in my room or to match with my speakers? 

(One challenge for me is that I'd like to buy something that will work well with future speakers, and of course I don't know what those speakers will be. So I'm wondering how to balance what I have with what I might have.)

I live in the mountains of Vermont so I can understand why my $25,000 Subaru is a "better" car here than a $250,000 Ferrari, but I don't know how to apply that to subwoofers.

(And if you're reading, bubinga, where did you audition/buy your Joseph Audio Pulsars? I am enjoying their website but I can't see if they have dealers. They're out of my price range for now, but I'd really like to hear them.)
Thank you, turnbowm. I've been reading a lot, including some other things from absolutesound, but that's helpful. 

I'm probably trying to take on too much by anticipating, vaguely, future speakers. And it's a bit tricky because my room is open and bleeds into other rooms, but my speakers are small. But I'm getting it, slowly!

"Second, choose an appropriate subwoofer for your main speakers and your room. If you have a 5.5" two-way mini-monitor in a small room, a sub with an 8" driver is more likely to blend with your mini-monitors than a model with a 12" cone. Moreover, the smaller subwoofer is less likely to overload your small room. The smaller the room and the greater the subwoofer’s output, the greater the odds against achieving a musical result."
In my opinion, you can purchase the best subwoofer you can afford and use it with your current system and in the future with upgrades.
I believe the REL brand is the way to go although there are other good manufacturers of subwoofers.
Hi northman,

What is the size of your room? What kind of music do you listen to and how loud? I have a 25’ X 30’ room and my single T7i (corner loaded) energizes the room quite well. Yes, you can overload the room with too large a sub.

Regarding setup, I found it fairly straight forward but you’ll need to listen and tune by ear.

And I have my Pulars on stands about five feet from the back wall. These type monitors (including yours) perform best that way versus putting them on the shelf.

Finally, I was considering upgrading to 3SHO or the 510 and decided not to do that.  Unless you have a large room, I would recommend you start with the T7i (not the 5i) and buy from Music Direct.  They offer a 60 day money back gaurantee.  That way, you can audition and determine if it's the right size for your room.  If not, return and try the next model up the chain.

Regarding the Pulsar audition.

I’d call Jeff Joseph directly and see what he can do. Yes, you can talk to the "man" himself. He does sell direct and I would certainly ask for an audition before purchase. And FWIW, over the last 25 years or so, I had four different Martin Logans before I switched to the MBL 116’s. Suffice to say, I was very skeptical regarding how close the Pulsars would come to the 116’s but found they got me close enough in all performance parameters so I was not, am not wanting for much. The REL contributed significantly to this outcome. The Pulsars and REL, assuming appropriate gear and optimum speaker placement, are stunningly good. By the way, I listen mainly to jazz and classical but still enjoy Dire Straits, Pink Floyd, etc. on occasion.  The combo performs well on all genres and can play surprisingly loud for their size.

Also, be advised that you can pick up a used pair of the "legacy" Pulsar for somewhere around $4K. Current model has the graphene coated woofer and retails for $9K. I would not discourage you from buying the legacy model since you can upgrade to the newest model (in the future) for $2,300 which I plan on doing this summer. Can’t imagine what the improvements will be because the original model, with the REL, is superb and performs well above its price point.
Thank you all! I feel schooled in the best possible way. bubinga, I'm going to pm you, if just to thank you for your thoughts.