Take a look at an SVS, Hsu, Epik, or eDesign sub. They all sell some very strong performers that won't break the bank. I plan to replace my BIC VK12 with an SVS PB-2000 or SB-2000 sometime soon.
BTW, OP: what kind of floors, ceiling, and walls do you have? (carpet, hardwood, laminate, drop ceiling, drywall, plaster, etc)
BTW, OP: what kind of floors, ceiling, and walls do you have? (carpet, hardwood, laminate, drop ceiling, drywall, plaster, etc)