Actually I own a Pass Labs XA 100.5 amp. It is quite good, but I also own a Clayton M200 amp and it is better in just about every category I can think of. The Clayton is the most true to the signal of any solid state amp I have evr heard. And it has 200 watts of glorious Class A goodness. The only other solid state amp I have heard that approaches it are the McCormack DNA-500's. The DNA-500's are a bit more liquid sounding, which isn't a bad thing, but not quite as accurate as the Clayton's. They are both significantly superior to any Krell's or Levinson's.
The above said, I would put the Clayton's and the DNA-500's firmly in Class A, with the Pass XA.5's in the upper Class B, the Levinson's in Class B, and the Krell's in lower Class B.