I did a bunch of jiggling of wires with the empeg out (you can reach through the sleeve) which seemed to make no difference. Put the empeg in, the headunit's phantom mute sensitivity is high, take the empeg out, headunit only mutes when the speakerphone tells it to. Doesn't seem like a loose connection. Could be voltage regulation as well, but even if so, that seems more like a trigger than the real "problem" of current leaking into the empeg mute sense line.

I'm going to pick up a couple of 1N4001s from the shack tonight and schedule some surgery for later this week.

Thanks Tony,
-brendan