Hiya mate,
The ipod adaptor is fairly easy to sort out, you can get a genuine Audi ipod kit or third party (kufatec or similiar) from ebay, just plugs into the back of the stereo and route it into the glovebox or even down in front of the gearlever if you have the ashtray delete kit..
Is the sub in the A3 an aftermarket one or the one fitted with the Bose kit?
If its aftermarket you should be ok with what you have planned i would have thought, if it's the Bose sub it may be a bit more complicated due to having the Bose amplifier
HTH
The ipod adaptor is fairly easy to sort out, you can get a genuine Audi ipod kit or third party (kufatec or similiar) from ebay, just plugs into the back of the stereo and route it into the glovebox or even down in front of the gearlever if you have the ashtray delete kit..
Is the sub in the A3 an aftermarket one or the one fitted with the Bose kit?
If its aftermarket you should be ok with what you have planned i would have thought, if it's the Bose sub it may be a bit more complicated due to having the Bose amplifier
HTH