I've owned Pass X350 and X600 amps, as well as X1 and X0.2 Pre-s in years past. Excellent SS Gear!
I never found a PC that outperformed the older Electraglide Fatman cables on these amps. The cables are unwieldy (very stiff and fold rather than bend) and the build quality is suspect, however, their prices have dropped so much that it may be worth your while.
The Preamps thrived on Synergistic Research Reference PCs. These are the older style without the ground stations and are not the "X squared".
Obviously these are not the latest or state of the art PCs, but you'd be hard pressed to out perform them at any price. Once I settled into these selections, I never looked back and was able to concentrate on my other components.
Good Luck.