Looking for a sub to compliment a 2 channel system

I could use a suggestion or two for a powered subwoofer to compliment a pair of NHT SB-3 speakers. Preferably in the $400ish price range. I dont need something very loud, but deep is a must as the SB-3s already go down to 40 Hz and there isnt much point in a getting a sub that only hits 10 Hz lower. I listen to most anything, Jazz, Metal, rock, some Vivaldi here and there even. Flexible placement is also a must because, quite frankly i dont have alot of room or convienent corners to work with.
Thanks, -Dan-