I am convinced that the Empeg digital circuitry ground currents are present in the audio output shields as evidenced by the fact that it will operate without any other ground.

I'm not sure what you're trying to say here. Are you saying "I can lift the ground on the empeg and it still runs, so I know they've got their audio stage wired poorly"?

If that's what you're saying, I think you're drawing the wrong conclusion from the evidence. What this tells me is not that there's anything wrong with the empeg, it tells me that you've got a serious ground loop problem that you need to solve. Have you run through any of the diagnostic steps in those PDFs that I linked in the FAQ?