Edit again: Oh, this just occurred to me; is one $400 sub better than two $200 subs? (I hope that doesn't sound like a stupid question)
That's not too easy to answer. On one hand, some would prefer the single, better sub, as they would say that once you give up extension, you can never get it back. These people who might urge you to get the better sub are secretly crossing their fingers behind their back, with the hopes that you will get a second "better" sub.
But, without crossing my own fingers here, I personally might go with two lesser subs, for the better response. However, at the $200 mark, the only sub that I know of on my own radar are the Dayton subs. Outside of DIY, it is in my rough opinion that subs start taking off at around the $500-600 mark.
Edit: So whats the deal with Yamaha and their "HD audio receivers" advertised on this site? Seems kinda funny to me, even without having the benefit of this new found knowledge. I mean to some degree electronics effect it sure, and apparently D-class amplifiers and tubes sound the best, but "HD audio"?
HD audio is surely referring to the new codecs available on bluray. They are "lossless", meaning that all of the source information that the audio engineers intended makes its way into our sound system. D class and tubes do not necessarily sound the best.
I've also heard that different receiver manufacturers sound differently, like Onkyo has the best mix, Yamaha has the best something rather, and Denon has the best other something sounding.
Yamaha is known to make very transparent pre-amp sections. Onkyo is known for both large feature sets and healthy amp sections (which also run hot, due to the intended design in getting more power),
for the money. Denon is known to have excellent implementation of advanced technologies, with good reliability, but at significantly higher price points.
Personally, ever since the advent of HDMI receivers, I've always looked towards Audyssey technologies, and so of the brands you listed, I'd cross off Yamaha on my own. IMO, Denon is more desirable with comparable models of Onkyo, but I find that I am on my second Onkyo, because I have found that Denon's comparable models are usually 50-100% more in price with receivers, and about 200-400% more with pre/pros.