I think in your shoes, I would start by asking your local BMW dealer technicians what they think is required by way of parts, fitting, and setting up of the system.
If the cost of the parts is eyewatering, then if you have no issues with it- I am sure that there are 'second-hand' parts on ebay from Lithuania, which may appeal. Your local BMW dealer might be okay with fitting and setting up.
If it is too prohibitive, an 'almost' halfway solution would be to fit the "extra control" cradle for the Nav 5/6?
Best I can offer, I'm afraid - other than to suggest a search through the archives here and on the US site?