The problem in selling them is that power is CHEAP these days and that old electrolytic capacitors wear out. While those amps are great, there's good odds some parts on it's board will begin to fail sometime soon. Best to just use them to run some front components (for which it should be adequate).
You won't get a great price on it, lose your arse in shipping it, then if it finally fails from age in a few months you'll look like the bad guy. Might be there are some old A/D/S collectors out there, but I would suggest just use it... really you may well get another decade out of it, but by my estimation the risk outweighs the reward trying to sell unless it's to a friend at a friend price, who understands what they're buying.