I'm happy to help. If I may offer some advice on understanding the total ownership cost of the OEM Nav retrofit, please enquire with the vendor and find out what they will charge you to re-code the system's integration in your car should the coding be wiped out by a dealership-installed software update. An aftermarket Nav installation, even an OEM one, is not considered to be part of the car's Vehicle Order by the BMW maintenance system and will be ignored during software resets or updates. It is possible, but not likely, that your car will live its entire natural life with the software with which it was delivered. If the cost to re-code is $100, or so, then no biggie. If it's many times that, then you may regret not having purchased a car with the Nav factory-installed system because you will hesitate to take your car in for service for fear of incurring additional and repeating cost.
I'm sorry to make this so complex. That's what you get for asking intelligent questions!
