The empeg wants +12V for mute, 0 for no mute, right? I'm pretty sure the headunit (Pioneer Premier DEH-750MP) is the same (unless it detects N/C differently than 0). I suppose I should test it, if the manual doesn't say.

I'll check out the emplode settings.

The issue with all 3 wired together was that the empeg itself *never* muted, the speakerphone would always work to mute and unmute the headunit, but randomly the headunit would mute itself and require a power off in the middle of playing music when not activated by the speakerphone (when this happened, using the speakerphone worked, but it would never leave the unmuted state).

thanks again,
brendan