Hi Andy,
The tv aerials are actually integrated into the rear screen on A2s and the amps are installed behind the tailgate trim.
There are 3 amps for the aerials (the fourth is a combined AM/FM aerial and amp) and they are available form Audi at a cost of about £60 each!
They all then feed into the correct diversity selector box (the standard one is FM only, not TV) and from there into the tuner.
Cheers,
Mike