To retrofit oem camera for a6 c6 you need to mmi module with fbas ( video in) if you dont have tv tuner in the car already then you dont have the correct mmi module. To change the module for one with fbas you would need to remove componet protection...
Apart from this you will need a parking sensors module that supports video...
And wiring, rear camera (comes with the lincence plate lights) , fit all in and code it .
Hope this helps 🙂