notes, OEM nav is retrofittable -- but it will not have the same functionality of the factory-installed unit. The most notable difference is that the map display in the right-hand gauge nacelle is not possible with a non-factory-installed unit. I believe voice control is limited as well, but am not certain about that ... maybe some of our Porsche-employed members can chime in on this?
From the TEquipment website:
<<Please note: No additional map display on the multi-function display of the instrument cluster. Please take into account the additional equipment scopes subject to charge if your vehicle is not equipped with voice control/navigation.>>
Also, the $2,200 price is for the unit only; install cost will be extra.