I am currently using the Car2PC adapter with Centrafuse (from fluxmedia.net) It works pretty good but there are a lot of features that are still missing and bugs that needs to be fixed.
I have looked all over the place, including emailing the support for Car2PC but I havent been able to locate the source code for it.
These are the current functions that are available.
Next Track, Previous Track, Disc +, Disc -, Shuffle/Random, Fast Forward and Rewind.
Thats all I can think of, but there might be more.
If someone find the Centrafuse source code please post it.