My brother just got a 2004 Cayenne S with NAV and I have a 2004 Cayenne, he is taking out the stock nav and cd changer and putting in an aftermarrket head unit and he told me that lets install his PCM in my Cayenne, is this possible? Both Cars are 2004 Cayennes. So I dont know if this would be called a retrofit

Thanks guys, 6speed is a fountain of information