Help! I've just bought a 2007 A3 Sportback (5dr) and am well disappointed to find that there are no rear door speakers and there don't appear to be any speaker wires in the rear doors either.

The current stereo unit is a single CD Chorus so i'm guessing this is the basic/cheapo model. Can I just run wires to the back of the existing stereo or do I need to get hold of a different one? I've seen some Concert units listed online but don't want to get one if a) they don't fit, or b) there's a much easier solution. If this is the solution, do I need a specific 07 plate A3 stereo or will any do?

Apologies if this question has been asked before etc. but i'm new here and am hoping some kind soul will provide a simple Janet & John explanation!!