Amp Replacement Recommendation

Hello. My current system is composed as follows:

- Cd player: Accuphase dp67;
- Preamp: Audio Research Ref. 3;
- Amp: Onkyo m510 Grand Integra;
- Speakers: Proac Response 4;
- Cables: all MIT.

I am considering to change the amp, which I believe is not proportionate to the rest of the components. Could you pls recommend 2/3 amps, which may fit with my system. I am looking for a powerful amp (to drive my proacs, which are quite demanding). SS is probably better than tubes. I listen to all genres of music (mostly jazz, blues, rock, camera). Max budget: $5-6k (used is ok). Thanks!