I just got M&K 850 series main speakers (similar to the 750THX series) and I need a sub for my HT which is in the basement ~13'x19'. I can't decide if I should get a matching M&K 150THX sub or a SVS 25-31 or 20-39. I like the sub to musical but clean down low. I think most subs will sound different in a basement because of the concrete walls so this may be a concern. Any suggestions?