I agree w/ JMS's response, my KAV400xi seems to have boundless power. I haven't come close to clipping this amp or pushing it to its limits. However, the amp is about as un-tube like as SS gear can get. Accurate, but a bit cold with a sharp glass-like edge. Not warm at all. It certainly exposes poorly recorded and mixed source material. I do like it, but I have a little sibilance in my system I'm trying to eliminate. I don't think it's from the amp, but rather power issues I'm having or from the source material, mainly CD's.
I haven't heard the 300 version in a few years so I can't comment.