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.

I would also consider looking for the XA60.5's at the top end of your budget. Always been impressed with their performance when auditioning at local dealers. If not for their size, I was considering switching from my current Rowland 312 to the Pass Labs XA100's.

Yes, I'm curious as to how the A21 sounds with the PSB's, and what models they are. For that matter, what's the rest of the system?

What is the rest of your system?

If you have balanced outputs from your preamp my Krell FPB 400 cx is for sale at less than your price range. Superb amp.