As far as *I* know (which means I might not know what I think I know) the differences are in the comms protocol between the head unit and the PB. There are a few in use in different make cars, common ones being K-Bus, I2C and CAN. What I definitly don't know is wether the PB comms is software driven or hardware determined. If it's hardware, you're stuffed, unless you swap your head unit to match the PB type.
Perhaps Phatnoise will tell you?