Amp suggestions

Man, you've got lots of great options at that price level. Here are some other good ones that are for sale here now and are in or below your price range:

Plinius SA103
Hegel H20
Gamut D200i
McCormack DNA500

Of course there's also the Parasound JC2 if you like your current amp. You really need to tell us what aspects of performance you're looking to improve and which are most important to you to get more specific and useful recommendations. These are all great amps listed here, so especially at this level it largely comes down to personal preferences. Best of luck.

Agree with Bob -- how do you know your sub is really "dialed in?" What method did you use? Does the problem occur with the sub off as well? Perhaps some more advanced room correction will solve the problem and you're done -- not sure what the P7 can do but DSPeaker another option. I'd try that first. This may well be a room issue and you may also try experimenting with some bass traps, which could also help significantly but I'd try the room correction route first as it could help in multiple areas.

Lastly, you don't mention what interconnects/cables you're using. They could also be contributing to the issue although likely not the solution. Best of luck.