+1 for the sub over new avr. $600 can get you some nice subs from Hsu and SVSound to name 2 companies with good subs in that range. Just don't use it turned up. A sub properly calibrated should not be heard over the mains it should blend in and smooth out the bass response and if the neighbors complain, only use it for movies and invite them over to watch \:\)

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70