Well I knocked up the "simple" interface version last night which should be good enough since nothing else in the car is Ibus (

)
Also I can't do track titles or anything fancy it seems (

again). I was thinking of a remote display although that will of course require a second serial port I don't have. It's certainly going to require some creativity on my behalf to keep the stock stereo. For now I think I will simply run the empeg into the changer inputs and I can probably work out how to send all the front panel buttons using the disc select options.
How long before you show us what you've got do you think?
Otherwise I think I'll start writing something tonight assuming I can get a development environment up and running.