Hmmm... When you are in that reconfigured mode (amp control and signal from the Sony), do you get any noise if you plug the empeg into the sled? In this state, the empeg would be fully isolated from the signal path and the amp control path, so that would leave only power / ground off of that shared connector that could be causing the noise. If you did not get any noise with the empeg powered, that would only leave the empeg's signal path as the source of the noise.