I'm not a big fan of the A21, to me it's always had a touch of upper mid edge that can cause the soundstage to collapse. Right now I'm really like my Electrocompaniet amps, they're one of the most refined sounding amps I've heard. McCormack DNA-250 would be a great amp in your price range, you can even find a used Bryston 4BSST2 for just a hair under $3000 and they're absolutely fantastic. If you don't mind used used there are tons of other great options, so many options in fact that it would be impossible to choose one as best.
Oh, and forget about anything Rotel. I just heard all their new stuff about 2 weeks ago and left with a headache ... very fatiguing.