Earl Geddes has a paper on the use of multiple subwoofers that is at his site. He shows that with 3 subs you can get response similar to 4 as Toole recommends.
http://www.gedlee.com/Papers.htm
The powerpoint on small room acoustics is very good that along with the pdf on subwoofer placement should help the OP.
The bottom line is 3 $400 SW would be better than 1 $1200 SW. This has to do with the acoustics of small rooms.
Arnie makes a good point about electronics and that there is a good understanding of what will sound good and what will not sound good. If you find as design where the distortion components decline in a linear fashion as the volume declines, there are lower levels of high order harmonics than low level harmonics, then the amp will sound good.
Money spent on room acoustics and placing speakers in a room will provide far more ROI than the latest magic cables or expensive amps.
http://www.rpginc.com/residential/index.htm
Since many recordings have problems a good eq for program material will provide a good ROI. See the Burwin Bobcat if you want to want to improve your sound in a meaningful way.
http://www.burwenbobcat.com/BBTB_Home.html
Wish I had the $$ to get one of these