Integrated Advice vs. Present Adcom Combo

My absolutely honest answer to your question is: I don't think that you will be able for $500 to significantly improve on your Adcom separates (assuming they are both in good mechanical and electrical operating condition). The 565 preamp, while a somewhat dated design, is still a decent unit, and there are not many moderately priced integrated amps that provide more than the 60 wpc of the 535. I think you would be better in the long run to defer the purchase for now, save another $500 - $750, and then "go shopping" for a good quality integrated amp.

Nait 5i is an excellent integrated that appears on Audiogon used for about $1000. I bought one to replace an expensive system and was very happy with it.

You can sell your Adcom amps to add to your $500 budget.

I second the Audio Refinement Complete (used). It has received very good reviews, and based on my personal experience of the Adcom GFP 565 (was a big bottle neck- killed by Creek passive), I think there would be a significant improvement.