In an Interview with Bob Carver the following question and answer I copied for brevity.
GB: How audible are the differences between solid-state amplifiers?
BC: What I'm going to say will fly in the face of what most people believe. I believe that you can take two solid-state amplifiers, and provided neither one is overloaded in any fashion, they'll sound identical. That's a big if. Amplifiers are overloaded in three basic ways. They're overloaded in amplitude; they've overloaded in current; they're overloaded in speed. It's very easy to do this if you don't have a big juicy amplifier. Obviously a little Radio Shack amplifier is not going to be able to touch a big Jeff Rowland or a Mark Levinson or a Sunfire amplifier. Provided the amplifier has flat frequency response and sufficiently low distortion, both of which are trivial these days, and provided there are no interface problems, the differences will always be the subtle differences associated with overload, either momentarily, like slew-rate limiting or clipping, or just running out of drive current.
Here is the link for reverence.