Justthis past weekend, I spent a couple hours comparing a Krell FPB300 with an ARC VK100 MkII. The Krell surprised me with its smoothness, and of course its low end was incredible. I never liked Krell, but this amp almost won me over. By the way, it was a demo offered at $5500! I have not heard the Pass, but I owned a Threshold 400A amp, an original Pass design from 20 (!) years ago until just recently. He makes nice stuff, that's for sure. Compared to the ARC tube amp, however, the Krell did not have the same degree of air and dimensionality. I am not a tube guy yet, but I'm close to being converted.
