Thanks for the advice. The MFWs are definitely on the list, though I just can't see a 15" sub being that quick/musical... I've been looking almost exclusively at 12" drivers. Unfortunately appearances are important so the HSUs and the SVS cylinders are out, but the SVS PB-12 Plus would work (especially with the Plus/2 on sale). Is that a clearly better option? I know this stuff is subjective, but I also know that almost any of these options are going to blow me away.
Also, having never calibrated a multi-sub setup, I AM intrigued by the Emotiva DRS-1, but obviously no one has had a chance to use it yet. I'd rather buy what is known when it comes to speakers (willing take risks on electronics though).
edit: oh, and definitely can't go MORE than 2 subs. Just barely got permission for more than 1.