I like your idea about going with the adapters if optical output is needed. I was about to offer that suggestion myself. I think everyone that expressed interest in an optical output said they wouldn't mind a dongle. Well, that adapter would then be that dongle. A simple voltage regulator circuit would take care of the voltage mismatch.

I had just planned to put the connectors, whether they were optical, I2S, or coaxial at the back of the Empeg. The docking ability would of course be limited by that solution. Sending the coax digital signal through the mic input cable sounds like a great idea too. Thanks for your input.

Update: I'm just about ready to order the parts for the first prototype. Probably tomorrow night. Once they come in I'll check the fit on the PCB printout and if all goes well I'll order the PCB. In couple weeks I should have the proof of concept prototype finished. Sorry things are moving so slowly, but school keeps me pretty busy.

Stu