Hi guys. I'm thinking of upgrading the system in the A3 so just wondering what set up they run as standard? i.e. front speaker size, rear speaker size...also am I right in reading these already have a small sub/amp fitted? Does this amp run the rear speakers and sub? Ideally I'll be fitting a new HU, front components with rear coax's both run off an amp and then a sub with separate amp in the rear...any comments on this set up or anything I'll need to be aware of? Any advice appreciated.