Just picked up a MY03 A4 Avant TDi 130 today. It has a single DIN Concert fitted. I checked in the back and there's a silver box in the side panel in the boot. I'm after fitting something like an Alpine CDE-104BT or JVC KD-R801 head unit as I'm used to having MP3's on USB memory stick in my previous car. What should I be aware of when getting the head unit changed (I will get it professionally done, I'm not keen on DIY with electrics). What wiring harness will I need etc. I'd prefer to source the head unit/parts myself so I can shop around for price. Will there be a problem with the radio aerial. Also if I get HU with a rear USB lead is it quite simple to route the USB lead into the glovebox or is it quite a job to get access into the glovebox. Thanks for any help Martin.