The suggestions you've received have been integrated tube amps and seemed to be geared toward you replacing the whole unit and not just the amp. While they're probably very nice amps, they don't seem to answer your original question.
I have the iDecco and use it with a modified Dynaco ST-70. It's more than enough power for my 93 db efficient Decware ERR's. You may find that you'll need more than my 35 wpc with the Focals (especially if you're going solid state).
I've tried out my Peachtree with my Sumo Andromeda II, and and Adcom GFA-5500 and 5802. You could easily find a 5500 for under $500 if you're prefer leans to the warmer side of solid state electronics. The Sumo occasionally sells in your price range. I'd suggest the Sumo if you prefer a more focused, detailed sound. The earlier Adcom GFA-555's will also lean in this direction, but I feel the Sumo does a better job with resolution and balance. The big winner in this group for me was the Adcom 5802, but they usually sell for over $800. It has the tonal balance of the 5500 with better resolution and bass (IMHO). If you can actually find one for $500, it's a great amp to have available and would be a big upgrade - not just in terms of wattage.
Others I've heard but not with my Peachtree are the B&K EX4420, Rotel RB-1080, and Golden Tube SE-40. Out of everything I can think of right now that would be within your budget, the B&K EX4420 would probably be a great choice. I haven't seen one for a while, but I've seen them sell for anywhere between $250-600.