A3 swapping tape to CD unit
 

Just bought a 2004 A3 SE, came with a tape unit. I've bought a CD unit & taken it down to Audi (few problems with the car need to be sorted) & as a good will gesture they said they can have a look at swapping the units over. But he said he can't guarantee this as it has a lot of ECU's and could take some time. Surely it must be a straight swap? Any advice would be appreciated thanks!