I've upgraded my chorus in my 2005 a3 to an alpine hu. All good so far just need to sort the rear speakers wiring block, which has six wires on it. The wiring diagram has come off the factory radio so don't know what's where. I'm assuming if I cut the existing speakers wires to joint the alpine speaker outputs they won't work.. Well they definitely won't if they are amped. There's no cubby hole in the boot but I could take the trim out to check for an amp.. Also where is a handy switchable live as the factory hu only had a permanent live and can bus.