While my system is out of my car right now (bad screen and hard drive issues):
I did have a working solution for steering wheel control -- it involved the use of a SWIX, USB-UIRT,
and lirc. The SWIX sends ir commands to the UIRT, which then sends messages to your box for lirc
to handle. Fairly straight forward.
Although, I will have to reconfigure this once I get my box back up and running...