Have you considered using radical low frequency EQ like Roger Russell does with his new line arrays? He uses columns of 25 3 1/2" TB type full rangers that he claims are flat to 25Hz in room, and I don't doubt him. While his system uses a dedicated EQ, you could probably use a McIntosh MQ-104 or MQ107...they show up on ebay once in awhile.I like this approach, as sub integration problems, crossovers, extra amps, etc. are eliminated. Also, I think overall bass response is much smoother everywhere in the room because you are using 25 spread out "woofers" rather than just one or two.