How can I get the hex codes the Symphony II sends to the cd changer and tell my empeg how to translate them?

THANKS

Get a logic analyser and spend a few hours watching it

Don't know if that information is available anywhere on the web. I was decoding the protocol for the VW changer for a while until I found somebody who had already done it.

One other thing... with the VW system, it's not really a synchronous serial signal, so you couldn't connect it directly to the serial port on the Empeg - you'd most likely need to have something else in between like a microcontroller. The Audi may be different, but chances are it's similar to the VW one.