I use a Harman Kardon Citation 5.1 amp, but check firsts for pops. I have a Pioneer Elite VSX-94 receiver and when I change channels the external amp makes a popping noise through the speakers. This may drive you nuts.
2 channel amp to upgrade Pioneer Elite Receiver
I use surround about 10% of time. In fact, I'm fine with built-in Elite's surround amps. The front two channels, however, seem a bit too neutral for my taste. I would like something solid state that is a tad warmer and fuller. I will hook this amp to the "pre-outs" of the receiver. Please give recommendations.