The 990's bass management is tricky. First question, what firmware version are you using? I had trouble with my sub bottoming out after I upgraded to the latest 3.11. This weekend I went over my channel settings with an SPL meter and the sub was too high. I turned it down 5db and now the whole system sounds better. Also, I don't know if you're handy with wood at all, but I highly recommend any of these "tuba" subs. http://www.billfitzmaurice.com/index.html I have the Tuba 18 and it fills my 11x25 basement no problem.