Power amp under 500...

Go with the Adcom. I have an Adcom pre-amp.

I would look into an Aragon 2004mkII...I know it's only a 100 watt amp but believe me it will drive most anything...it's like some say "they are like a baby Krell" and built like a tank! you could probably find one on A'gon for in the $500.00 range...and if you want to spend just a little more ($600-700) definately look at the 4004mkII

Go an extra hundred
Look for used Rotel RB-1080. Decent balance of strengths,not old,easy to sell.

Either amp is fine. You'll do well with whichever you choose.

If you are looking for SS - the B&K EX-442 or 442 Sonata (later version) is an awesome sounding amp that is underrated imo...I owned one many years ago and it is extremely tube like but dynamic too...200w into 8 ohms, 360w into 4, 75 amps peak to peak...worth checking out if you can find one used, thanks, Louis