Clayton M300's vs Pass XA 100.5

I'm considering these two fine units. Besides the difference in power, might anyone have insight into comparative sound quality of these two full class A amplifiers. I plan to use a VAC Ren mkII to drive either in balanced mode. Also if anyone has insight into how the Claytons squeeze 300/600 WPC into 8/4, vs the Pass Units, I would be greatful.

Brian