I'll jump in, since I have absolutely no investment.
As the owner of an all or nothing system (it's TV by itself, or else I run through the stereo but that's really just DVD player feed) with a Bose soundbar, multi stereo speakers (PSB mains, as well as Cambridge Sound duos of satellite mid/tweeter and subs) and then dual surround (my old Infinity 3 ways topped by Bose satellites) I'm out of the loop on a TV reinforcement-only concept.
I did read an article on Crutchfield listing the soundbar - stereo - multi-speaker (surround/sub) options. It looks like some multi speaker groupings are under $100. And considering you're already out some cash I'd guess you'd want a suitable and cost effective method.
Bill, are you looking for "movie theatre" sound, for watching films (and music related media?) with deep bass and stereo.. or more of a TV reinforcement (richer deeper but basically just whatever the TV feed is.. meaning dialogue for the most part?). Plus space considerations; I've got my soundbar set behind the TV, on a shelf. And really just for the center channel feed, of surround/theater settings. It may be the typically most space efficient soundbar solution is going to be tough, due to the spacing below or around your set. The Bose I have isn't too tall, and I got it as it fits in well (plus Bose tends to throw the sound around, by design). A sub might be added to a soundbar, as one hybrid. Or I could see going with stereo, if you're figuring speakers away from the set. Although you might lose the dialogue and center channel focus (unless you want to keep with the TV speakers, too?).
It does interest me, just to watch what TV-based options there are for building that feed and going with self-powered additional speakers. Really, my plasma sound is fine, and I haven't found it "shallow" or lacking. And I always modify the sound as well as video. But as you noted, small plastic enclosures pointing away isn't going to be very hifi.
I could see the industry really going with a serious compatible TV speaker solution, with full fidelity speakers and a sub and enclose them with a TV in a big wood cabinet which
hold it. that probably isn't going to be cost, or space, effective. scratch that.
Ace; half the time I'm listening to the stereo or tv from another room, so what the hey.