Amp shopping - recommendations anyone?

Hello all. I'm thinking of treating my system to an amplifier upgrade, and would really appreciate some advice. Here's my situation.

Currently running:

Aragon 4004 Mk II
Aragon 24k Preamp
Rega Planet CD
PSB Stratus Gold i Speakers
Kimber cable throughout

I'm very happy with my PSB's and my Rega and don't plan on changing those any time soon. I'll probably tackle the preamp and cabling sometime down the road.

Things I'd like to improve in my system's sound:

- Currently a bit on the warm side
- Bass could be a little tighter
- Would like it to be "faster" (want Linn timing with PSB headroom)
- Soundstaging could be a bit better defined

I'm budgeting approximately $2,700 for the amp upgrade and am strongly leaning towards used. Contenders would include:

- Krell KSA 250
- Classe 301
- Pass Labs X250
- Bryston 7B ST
- Others?

Looking forward to any feedback or advice.

Thanks!