I currently have a Denon x2000 and a pair of Klipsch R51M hooked up to them. I was wondering if I should replace it with a stereo amp to get better stereo performance. Which stereo amp would make a meaningful upgrade in the same price range?

I know that in the same price range a stereo amp preforms better than an AVR. Although if I would buy a new stereo amp for a bit more than I can sell the Denon for, would I get better quality stereo sound? For example would an Onkyo A-9010 or a Yamaha 303 be better for stereo music?
IF we are looking at the second hand market what could I get for the money I would for the Denon?