[sajunky]

Based on this, is it acceptable to use the GFCI adapter in the wall and a three way tap to plug the two amps into it? Or buying a multi outlet GFCI adapter? I don't think a tube amp needs surge protection the way a PC does.

If you want GFCI, follow this:

wall plug --- GFCI --- surge protector --- multiplug    | --- device 1
                                            | --- device 2
                                            | --- ...
                                            | --- device n

If you don't, I can't help. Then if you still have hum, removing ground pin is a good idea. Moving a ground to a single reference point (in this case your PC enclosure) makes it 100% safe. If you want a thicker wire, I have nothing against. If it don't help much, you must take further steps as below.

If you still have hum, then you should work on redirecting ground loop. Current flow the easiest path. You don't want to be your RCA cable. You took my attention that your solutions work better, including running cable extension to another room. It is doing some form of redirection by spreading of EMI noise to another room, creating easier path, but it is completely uncontrolled.

I proposed already that if redirecting ground to the PC doesn't help, you should use ferrite clamps on your RCA cables. It creates impedance for a common mode noise on this connection. With ferrite clamps main current flow will be redirected to the ground wire between PC and the amp. There are more sophisticated methods, but all of them use the same principle. I use in my setup (between Audio GD R2R11 and amp) a custom cable that consist of a twisted pair (two wires). One is carrying signal the other is a ground wire. Twisted pair creates impedance against common mode noise. The cable is shielded, but shield is only attached to the ground on the amp side. the other side is not connected.

 

[BackwardPawn]

Thanks for replying. I forgot you mentioned the ferrite clamps; I'll try to locate some of those and see if it helps. I have no problem moving the GFCI to the wall. I would install a plug in the wall, but I don't own the apartment. I'll try this out and see if any of it helps.