What makes the difference in these two amps

I recently bought a B&K 202.2 amp to replace my Carver TFM 24. They have very similar specs I believe, but the sound is dramatically different. I've had my Carver tucked away for a few months and decided to sell it locally. After listening to the B&K, which I realize is not exactly top of the line, I plugged in the Carver to make sure everything worked before I sold it. It sounded like a clock radio until I got way up in the volume, almost like it didn't have the power of the B&K, not to mention the lack of nuetrality and it's annoying distortion. These are the only 2 amps I've had, with the exception of a Yamaha MX 1000, which I blew in the early 90's. So my question, why the big difference in sound, and what do I look foward to as I upgrade up the food chain?