I would suggest spending that amp money on a new sub like the EP350 or EP500 (or higher) or one from any of the other notable sub companies out there. You would most likely notice much more improvement in SQ this way than with an amp, JohnK covered why.

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