Need Help upgrading a MMI 2015 A6 Premium
 

I have a 2015 Audi A6 Premium, my question is, my car does not have GPS or reverse camera, MMI GPS unit according to my search on the Internet should be the 4G0035746H but is not what I have, or I think, I have been seraching on ebay and some peoples have different OEM (genuine) used or new units from 2012 to 2015 with the same number changing only the last letter. Maybe I should buy the connectors only or I should change the MMI unit? I've been looking on the internet to modernize the unit but I do not know and the dealer here they say they do not do that because the MMI units come in that way from Germany, there is any way to change the radio unit and put a GPS? I guess I will give an error code and have to take it to the dealer or if any of you have experience and can tell me to do ?, I need your help. Thank you and I hope your answer