After looking extensively at retrofitting the bmw satnav (and I even bought some of the parts), I backed off and fitted an aftermarket unit. I chose a Pioneer AVIC N4. The full satnav would have cost me $1100 to retrofit, with doing all the work myself, and the Pioneer option, with bluetooth and Sirius radio accessories, cost me $950. Not a big savings in cost, but I actually decided I would prefer to have aftermarket. The BMW satnav for the Z4 is simply too dated and antiquated. By going with a DIN HU with flipout nav monitor, I am adding both newer and better screens and maps, and a better stereo component to the car (I'm a stereo nut and also run a big amp and fancy german 3-way speakers). I am also ensuring that if better-and-newer satnavs come out in the future, I can easily upgrade by removing and selling the old one, and sliding in the new one with minimal effort and re-wiring.