Donnelly asked:
"Other than power, do you think there are any differences between the KAV-250a and KAV-500?"
I don't know, my best guess would be that they sound a lot, a like. The biggest difference in sound, between amps cut from the same cloth (IMHO) is the difference between their power supply/transformer size. This would come into play (or not)...depending on the speakers used, room size, spl's required...ect. At normal listening levels (75-85db) I would expect, that the Kav amps sound similar.
The Kav-500 "does not" sound like the old Ksa-250 I had. The Ksa-250 had a relaxed tonal presentation...the Kav-500 has a more forward sound, more detailed (lots of twinkle)... I never thought it bright though. I liked mine.
As I mentioned above, though. If I had speakers with tweeters, that were "a little over the top" in the treble area of reproduction....they would now be, more so.
You could try the Kav-500?...the three channel Kav goes for around $1,300-$1,400 used...pretty easy to sell, easy to ship if you don't like it, (50 lbs or so).
I paid $1,400 for mine, sold it a couple years latter for $1,400.
Dave