Alright, here's the skinny on all of this...
....First, all things being equal, there are several very real advantages, especially in a strictly HT context, to using full range type(or even not full range for that matter) speakers with powered subs built in to the speakers themelves(not even consdering full active types here at the moment). The first advantage of this kind of design, over your standard passive full range counterparts, is that your effecively "bi-amping" your main speakers! Your taking the bass strain off your main amplifier(or receiver, as is often the caes with these types of speakers), and letting the power amp in the speakers handle the more dynamically demanding bass frequencies. In and of itself, all things being equal between standard passive full range speakers, and speakers w/powered subs built, you'll almost always find that the later sounds much much stronger, and more effortlessly dynamic than your traditional speaker offerings. Also, the benefit of having the powered bass amp sitting electro mechnically "on-top" of the bass driver itself, makes for a much higher damping factor, and thus more control over the driver itself. Even if you were to take the competing passive full range speaker and "bi-amp" it passively, you'd get stronger results than normal usually, but still not competetive in the afore mentioned area's as what you'd get from the "powered" active type speaker. Especially, also, when your considering that most people who buy these kinds of "powered" towers are going to use the with relatively low powered receiver amplifiers (no receiver can compete with even modest separates power wise), the "powered" speaker here has even a larger advantange, and effectively make the receiver sound much strnger, even surpassing strong separates based systems driving stadard passive speaker systems. In addition you'll find that the average standard speaker people end up using is your standard stereo music speaker design, which is relatively low sensitivity, lower efficiency, harder to make sound dynamic(esecially compared to what a ulra high sensititivity horn loaded theater speakers are doing with DD/DTS in comparison!..), and much to laid back, polite and univolving sounding for more accurate HT playback and soundtracks! These speakers were never really designed with a dubbing studio's digital soundtrack mixes in mind when they were conceived!...and it sure shows when you try to play back movies through em realiticall.
Again, the advantage in control and sensitivity increase that you gain from "actives" will, in my extensive experience,in homes, an store/show room demo's, and expo's, etc, will still outway even more ambitious traditional speaker/separate's amp'/preamp set-up's dynamically!
Personally, I think the "powered speaker" w/at least active subs built in, are the very best thing to happen to "receiver" based systems! Receivers on their own, alway's having limited usable power current compared to stronger separates amplifiers, can use all the help they can get, and "powered speakers" offer this kind of advatage to the receiver user! yes, you can still get even more dynamic sound wih even adding a separates based system to those speakers, for advantages dynamics through the rest of the frequency spectrum as well.
Now, yes, to an extent, you can largely get a lot of the benefits of what I just described, using a passive speaker set-up and integrating a sub(s) to the speakers, and do some augmentation that way. But it almost alway's sill not as effective in the dynamics area especially if your still ssking the main speakers to run full range, with lest gusto and slam on their own. Now you can improve on this greatly by using "bass managment" wich most all current pre/pro's or receivers offer, and effectively let the bass be handled by a powered separate subwoofer, while only sending uperbass/midrange/treble to the mains, and that does help the dynamic spectrum out greatly yes. However, ultimately what you'll find is that, set-up and integration between the speakers and sub's, leaves quite a bit to be improved upon in this scenario! Usually what you'll find in a well integrated "powered" tower speaker, is perfect phase coherence, and complementing between all th drivers and crossover points, which yields a superior dynamic pressentaion, that's also stronger and more in-step acoustically! Thusly, where the bass drivers and midrage drivers crossover in this design, you're also getting driver overlap, which further steghthens the dynamic of the shared frequencies that are being covered, and pressents them in perfect symetry and time domain. 99.9% of the time I'd submit to you that, even with multiple placed separate subwoofer set-ups in the room, couled and crossed over to stanard passive speaker array's, that the cohesion, phase, and coupling (not to mention proper placement in a room..that's another story) of that set-up ALMOST NEVER is pulled of as well and as authorative, tight, and controlled as a prefectly integrated "powered tower on it's own!...all things being equal of course...you can get bigger/badder/faster subs and such, but then you gotta know what your doing still to make it sound right.
So, all in all, unless your talking about ultra high sensitivity "horn loaded" high efficiency full range speaks(yes I said speaks), which in and of them selves have more natural effortless dynamic to their sound, simply do to the ease of efficiency, all things being equal, you'll find that powered towers have a bunch to offer the HT enthusiest, looking for a strong "real theater" like dynamic movie experience! whithout resorting to more traditional "theater horn" speakers, which have their dissadvantages and advantages on their own And, you can even, yes, add other external "powered sub's to augment thing even further. Infact, depending on how ambitious the "powered subs" in your speakers your considering are, you may still want to, in a lot of cases, still consider adding LFE subwooer action to the system, and let the powered speakers run more full range.
What I often still do with systems I set-up/install, when using full range powered speakers, is to still use some "advanced bass managment" that's offered by a number of pre/pro's and receivers out there, and cut the main powered speakers off at anywherer from 35hz to 65hz depending...and let the LFE subs and such fill in the bottom. When you can balance the bass between speakers and subs well, you'll find that they both will carry their prospective loads better, and not have one doing more/or less work than the other!
So, in summing, all things being equal, I've found that the most powerful sounding (we won't talk audiophile purity here...another story yet) HT speakers offered out there, effectively, on their own, are either "powered/active" type speakers, and ulta high sensitivity full range horn type speakers. compared to your average 2 channel traditional stereo speaker fair out there, really it's no contest for all practical purposes, and all thigs being considrered. I know can sell someone a simple receiver, and a set-up consisting of some powered's with some active subs built in, and they'll end up with a very powerful, dynamic, and hard hitting sounding speaker system, that sounds authoritative even at low volume levels, with all sorts of listenting material...Rock?...you bet!
And, yes, you can get your subs tidily stacked into one enclose if need be as well. You still can't substitute for proper speaker/seating placement and set-up however, and correct tunning of your system(including care and knowledge of how to set things properly on the gear). A lot of knowledge and experience still go's a long long way in trying to get a more world class/high end audio pressentation...even from the best speakers and equipment in the world! I'd say that probably 95%+ of all the audio enthusiests out there usually end up with mediocre to poor overall results, with ANY GEAR/SPEAKERS, in a given room, simply because they don't know what their doing. Dommestic living rooms and basements and such are really a lot more aousticlally challenging(especially for multiple listeners) than proportionatley larger acoustic venue's such as commercial theaters, clubs and concert halls. And they thus require more attention and care to make your investement work.
So, back on track, really I do strongly, as a tool, highly suggest some of the fine "powered" speaker offerings availabe out there. They sound very very dynamic, offer a wide range of flexibility and potential, work well even with modestly powered receiver based systems, offer higher sensitivty usually(which lends itself to a more effortless dynamic), and let you control the bass output more for even more precise speaker placement when you "must" place things in one place opposed to another.
Also, I noticed that most powered speakers offer you the ability to connect to the bass woofer via RCA "line-level" connections,as opposed to simply letting the bass signal be tapped off the full range speaker wire connecions. What this allows you do to do, for the more tweeky of us audiophiles, is to put an "EQ" in the path of he bass woofer only! You can simply loop a good Parametric EQ,or whatever, into your bass woofer, and get some really pretty flat and rock solid sounding bass response doing this! This is an area that most peoples systems perform so poorly is even frequency response from the speakers. One thing that EQ's do do however, is mess a bit of the audiophile purity qualities of the midrane and treble usually. So, the ability to cure alot of the bumpy and lumply bass reponse, while not brutalizing your all important and pure sounding midrange and treble purity in that specturm, is an attactive thing. If you don't know what you're doing however, you can do more harm than good, but the option is easily there with this kind of feature on "powered speakers" and subs. Infact, I highly recommend quite a lot of times people should consider EQ'ing their sub woofers if they can afford the time/money/effort. A good Parametric EQ on a sub which is foundationally well placed, is a killer option on the quest for more top caliber bass response from a system!
Oh, you also metioned the "con's" of powered speakers vs. standards. I do find that a lot of the speakers with powered subs are strictly in the "mid-fi" range of speakers. Yes, you really won't find some of the higher end music speaker manufacturers offering "powered speakers" in their line-ups, and I'm not entirely shure why...other than perhaps cost and R&D and such. Companies like Linn, PMC, M&K, and ATC, make some more higher end type, audiphile purity/detail type speakers, that not only have the advantages that I mentioned from the "powered" design, but offer more audiophile niceties that the purists desire. However, from a movie soundtrack/playback standpoint, a lot of what a good movie mix has to offer is not really exploited by your ultra high purity speaker designs. The mixes are alway's less refined, than say your better 2 channel audio recordings and such, and the things you want your HT speakers to achieve are WELL covered by a whole lot of mid-fi HT speakers out there, that do what a goot HT speaker is designed to do! Hard hitting dynamics, dialog intelligibility, focused soundstge, wide(but not too wide) off axis soundstage, limted vertical dispersion(a lot depends on the room your in here), and fairly good sensitivity designs are all in the plus for a properly conceived HT speaker. Your average audio first type speaker will usually be limited to certain applications for HT dubties effectively(to do things best that is), and offer a more music recording oriented, laid back, more polite, less foreward and involving, less dynamic sound pessentation, that's not really adept at handling DD/DTS caliber movie mixes as well.
Speakers that, on their own you might want to look into considering?...well I won't touch that one. After all they're not paying me anything to write this...So there you are.
Bottom line, someone who's experienced and skilled at working with all these kinds of speakers, in all kinds of rooms/settings, can do work magic with even the most unlikely gear in a room/system. Better gear?...even better Proper gear?...most defnitely a plus. And, from my experience, thousands of sales and hundreds of hook-up's/install's later, I like quite a bit of the powered sub type peakers I've come accross quite well for a lot of my HT applications. There's some really good designs out there, that sound great overall. They're very strong, very exciting, easy to drive, very equipment flexible, and pack a lot into one cabinet, yes. I don't alway's recommend them for all applications, and not every room can accommodate full range towers of any sort, and do do better with smaller satalites and sub set-ups. So, it does depend on the room it's going in and the appliction. No one speaker works in all situations, and it's all balance!
But, to generalize, I think you would get a very good HT speaker in a lot of the powered choices out there, yes....but it depends. Hope this helps.
Hey, tell me about your room...
