John E. Johnson, Jr. has posted a review of the Pass Labs XA-100.5 pure Class A monoblock power amplifier ($16,500/pair) at Secrets of Home Theater and High Fidelity. His conclusions:
A marketing department would definitely have specified this amplifier as a 175 watt output amp (maybe even stretching it to 200 watts). Nelson Pass chose to remain conservative and specify it according to the amount of Class A ouput it has, which is 100 watts. Most of the time, we only use about 10-15 watts. It is only with the transients that a lot more power is needed, and the XA-100.5 has that; it's just not all Class A. The amplifier is characterized by low-odd-ordered harmonics, which to my surprise, sounded great. That is because Pass designed it with this in mind, instead of a poorly designed amplifier that has a lot of negative feedback which may flatten the frequency response but also results in higher-odd-ordered harmonics (9th, 11th, etc.), and those would degrade the sound quality. Let's call it "controlled distortion". A fine product from a brilliant designer.
You can read the full review here.