Looking at this a bit more, it looks like you don't need the raspberry at all, it appears to be there just for the xbmc and sd/video/mp3 storage, is that correct? The MC is the clever (very clever) bmw interface?
Also is the attiny2313a-su programmable on the board as is?
53, M3, Silver Grey. Reto-fits: Modded Mk4 DVD, OEM Bluetooth, VR Control, Rainbow/Alpine Speakers, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.