Thanks for the response Tony. Let me explain myself a little better. I wish to use the factory radio as the tuner for my Empeg, I don't really feel like spending $300 for a tuner on ebay. Plus my car has a heads up display that would still function if I use the factory tuner. My plans are to hide the factory AM/FM cassette down in the center console. I would remote the LCD from the radio up to the upper left of the dash where I have a factory driving light switch that would be removed or relocated. I would also have use of the factory heads up display for radio functions only. My only way of controlling the factory radio once it is hidden would be with the steering wheel controls. I would then build a multi-level interface so the 8 steering wheel functions could have 4 different "levels" of operation (or 32 commands total). Level 1 would be Empeg functions only, Level 2 would be factory radio functions with Empeg volume overlay, Level 3 would be my remote radar detector which is already mounted inside the factory trip computer module. Level 4 -- not real sure just yet!
If the Empeg could output the source over the serial port, I would be able to read it and automatically switch the steering wheel fuctions between levels 1 and 2 without having to use a button to manually switch between levels 1 and 2.

Hopefully I am not too confusing...

Nick