Unfortunately my empeg is not used in a car any more - this would have interested me back when I did.. This should work quite well. It shouldn't be too hard to get some button presses one way to it and track data from it on to the screen.

Have you tried it in a running car? Whilst experimenting with other interfaces I found they were a bit susceptible to ground loops etc and so alternator whine and other interference might be a problem.

Nice one.