Adcom amps are a great deal used. If you got lucky a Threshold would be a real find. I would avoid Carver, they are not the most reliable amps.

For a budget amp you might look at the Emotiva for new.

For $500.00 you can get a decent DAC for Arcam or Cambridge Audio. The Schitt are coming on strong with performing beyond their price. The guys are from another large company, I'm thinking maybe Theta but not sure.