I got the Pyle PHE 400 and tried it today using the 4CM, with a Marshall Plexi, Fryette PS-2A, 4x12 cab, and Axe FXIII.
I put the Pyle PHE-400 between output 3L and the front of the Marshall Plexi.
It works! The ground loop squeal is gone!
I set outputs 3 and 4 full up on the Axe FXIII, and set the FX level on the Fryette PS-2a to low. So far everything is working as I hoped it would. (I used all regular cables.) I have two humbuster cables but I wanted to try it with regular cables first. It appears I might not need to use the humbuster cables.
Problem solved!
Amazon product ASIN B00BARTW42
I have yet to try the Fryette PS-2A as a silent load box. Have any of you used it for that successfully?