TT mk1 concert "tape deck" to concert "CD"

[A3SBQ]

Hi.

Hope some one here can help me.
I am helping out a friend that just have purchased a TT mk1 1999mod.
The car is equipped with a concert tape deck head unit.
The unit is faulty by haveing a bad connection in the volume up/down nob.

So now we need to change it.
1. Doese the concert "CD" swap directly in?
2. Can I use a unit from a A4 car!
3. Does it need any coding?
4. What is needed to get Aux-input

Thanks for helping.