Even more weird is that I just got done reading about a
similar situation from another thread. Klipsch was involved again. I was more focused on the
Outlaw 975 pre pro that I had bought and its purportedly low output voltage. It seems like I should have immediately made the association but I've been doing stupid stuff a lot lately. Anyway, as was suspected in the case linked, I think it's a combination of sensitive speakers, low output voltage and a low gain amp that causes your buzz/hum.
Let me ask you if your amp and pre pro have a mix of 2 and 3 pronged power cords. The linked thread has a suggestion, from TLS Guy, to lift the ground on the amp. That might help you use your Klipsch speakers.
EDIT: The
S&V review of your GFP-565. The listed output voltage is 2.0 volts but skimming the measurements doesn't show me that the spec was verified. I'm hoping one of our resident brainiacs will enlighten us both as to how exactly this works. I'm starting to think that calling them brainiacs is counter productive.