Another vote for Axiom sub over anything else. I've got an EP500 ,much better than the PB1000 I used before it.
Well I still use my PB1000 up against my couch as more of a mid bass unit. My Axiom is the big rumble and SVS booty shaker.
When I was only using M3 and M22 for my fronts the SVS seemed like enough. When I added my M80s the poor little SVS was completely drowned out by the M80s alone. The difference is night and day, the ported SVS runs out of steam easily and easily goes into chuffing . My EP500 handles everything fast controlled detailed. Never once an off sound. For the last couple years I've had mine.
