Best integrated for $500?

Rogue make a very good-sounding, very well-built integrated and I bet you would be very happy with it over your Onkyo. It's the tubes--they just make music so liquid.

Even tube amps don't all sound the same, though, so here's another suggestion, just in case you get the chance to compare: an Audio Space AS-3i. It sounds lovely too, but different.

And of course there are more.

Asking your question on this forum is sort of like asking a fashion designer forum who makes the strongest shoe strings.

I think you need to look (listen) hard at your local brick and mortar electronics store and you may be pleasantly surprised by something with a household brand name. You might also be surprised how well your existing Onkyo performs against audiophile brand name components.

All that is not to say that I don't really appreciate the cool factor of some of the components already suggested in this thread. I just think that when you want excellent amplification for low investment, the efficiently mass produced receivers are the way to go.

Or, you could buy a Nad or Arcam:).

Have a listen to the Yamaha A-S500? WhatHiFi had only good things to say. Buy.com has a great price on it. I would also check out the Rega Brio 3.

Audio Refinement Complete. Very stable at 4 ohms, rated 50 to 8 and 90 to 4. Neutral, solid bottom, grainless on top.

Used jolida 302