I have the same question. Seems its just a different screen and control module. I called a LR dealer and the parts guy said the dealer might not touch(programming/updates) it if I replaced these items because it doesn't match what the VIN states the vehicle is equipped with. That doesn't seem right though. Its an option on the car and if I pay for the proper parts, why wouldn't they touch it. Lack of warranty I get, but if I'm paying them to program a module, why not?
i called 2 dealers and both said the 10 inch has to be installed when you buy it. Not possible to add on. I had the tough choice of 2 cars and one had the 10 inch and 850 watt stereo. I decided on the 8 inch for other reasons. Hopefully I wont regret it.