Might I recommend the HSU STF-2.
It is a superb subwoofer. My system consists of M22's, VP100, QS4's, and a HSU STF-2. I am extremely pleased.
Not only this, but HSU has a
20% off sale for the STF-2, which knocks its already amazing price of $400 down to a very manageable $320 with $30 shipping.
Since your room is a little big, you could go for the
STF-3, which is priced at $480 (originally $600). I would jump on the STF-3. The STF-2 is acclaimed as one of the best budget subs...and if you can upgrade to the STF-3 for $80 more than the STF-2 price, that is an amazing deal.
That's what I would get.
Good luck!
