Let me echo Tvad. I have not been able to hear either in my own system but from other sources it is clear that their design philosophy is quite different and their sound is quite unalike. Pass has their own sound, class A has a midrange that you can't get from AB. In the past I used Krell, Musical Fidelity and Stax class A amps. I now use AB, Musical Fidelity and Meridian. The main thing is to decide what your sonic priorities are, no amp is the best at everything. If you can't audition them at home read the reviews and see which of them matches what you are looking for. And Buy Used, a high quality amp has a long life. I have a Tandberg 3026 that I bought used as a sub amp 15 years ago and it still works fine.