Aerial signal amplifier - A8 D2 FL

Does anyone know where the signal amplifier (for the radio aerial) is located on a 2001 A8 (D2 facelift)? My radio has poor (almost non-existent) radio reception and I've been told the most likely culprit is a faulty amplifier (I've already replaced the aerial mast itself to no effect). I've also I've been told that there may be more than one amplifier (possibly 2, maybe even 3) somewhere between the aerial and the radio head unit - is this correct?

Without more detailed investigation, my local Audi dealer isn't exactly sure where the amplifier is on the D2 - or even whether there is more than one - so hopefully you guys can help. Is it an easy job to remove and replace?