If they are BMW factory fit stereos, they are likely to have an IBUS interface. (unless they are old second hand ones). If they do then do a search for IBUS and BMW, the are some interesting threads on that.
I foud this on another forum hier
You need to be Yahoo member to enter.
The question was
display radio on pc how?
Answer that I got:
The I-Bus analyser recieves the data over the serial port, so you just need
to add the COMM control to your VB program, recieve the raw I-Bus data from
the serial port and then decode the protocol yourself in vb. There's plenty
of info around on the offsets that contain certain data within the I-Bus
I realy starting to believe that this is a good solution for a car pc solution.
The sound goes direct to boxes and we can also conect the Carpc sound to it, we can also use the BMW DSP and so one...
I've been playing around with the USB IBUS interface from http://www.eedesignkits.com to see if I can use my MID buttons that currently control the radio to control the computer. I was hoping I could send commands to the computer and maybe even display the mp3 song being played in the small screen where it currently displays the radio station.
I've been able to read/write to the MID the commands but I was thinking that once I remove the radio completely, and leave only the MID, that it will not work anymore. The reason I'm saying this is because it looks like the MID is pinging the radio, and I'm afraid that once I unplug the radio and the MID does not receive a ping back that it will stop sending signals.
Has anyone tried this? I know you wouldn't need to if you have a touchscreen but I was trying to see if for songs I could leave the lcd screen hidden away.