I've just bought a '99 A3 SE (does that make it an 8L?). To my total dissbelief having fitted my Sony MP3/CD I have found my car only has 2 speakers! Looks like that is the original spec. Can i retro fit rears? What size are they? There are no wires so I'll have to run them, while I'm at it I want to run all the cables for my amp and sub. Any hints and tips will be welcomed.