This is pretty neat, and its nice that I already have all the pre-reqs :-). Although I'm wondering if I have to use the analog cable for the radio as I've got the USB one, that will be a bit of investigation.
After a bit of prodding I caved and bought an aux cable, but I've wondered the same about the audio -> USB cable. It think it's FTDI so I think a clever person might be able to figure it out. If you get anywhere with this let me know!