I don't know what kind of main speakers your using, but you might want to try setting them to "small" with a 40 or 60 hz crossover, at least as an experiment.
I'm using large Polks with 8" powerd woofers that are supposed to go down to 30 hz, but I find that I get the best result setting thm to small with a 60 hz crossover and letting the subwoofers deal with the deep bass.
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HT:
990/770
Oppo BD83SE
Pioneer Elite DV-47A
Magnavox HDMR513h DVR/DVD-R
Sony DVD megachangers-2
Sony CD megachangers-2
Monster power centers-2
Sony 48" rear projection SDTV
Roku video player
JVC AL-A158 Turntable
Polk RT-2000s,CS-650,XS-650s,RT80s
LFM-1EX
Hsu VTF-1
12" Velodyne
Family room:
OPPO 970
Sony 32" direct view HDTV
Denon 3801
Rolk RMs