You will need a TV tuner and 2 TV aerials that fit on the rear side windows on the Avant.
The biggest issue is that the TV tuners for this are all a nalogue. This will make the system redundant in about 2 years as all will move over to digital transmission .
Sorry about the spelling mistake but the system does not allow me to type a n a l o g u e
If you need more info on installing the system, have a look at the following forum
vwNavi - Powered by vBulletin
Just follow the Audi link