If it humms out the speakers it's a ground issue, I tried a hummbuster also and it didn't work for me so it's not a huge DC problem. The Pass's already have a DC filter built in.
Have you tried the preamp at someone else's house to see if the transformer humm problem or an interaction/power/ground problem. ARC has great support.
Try floating the ground on the CDP, and then preamp , and then break the ground on one of the amplifier monoblocks (not both).