Hi James
I went to a local car audio shop, it would seem the system has no upgrade options as all the wiring is now fibre optic, speakers seem the only upgrade but this wouldn't achieve much as there is no control of the sub and they think Audi have locked the amp and think the sound is good enough, the only option I have after a lengthy chat with the audio guys is to replace the whole system, that would cost 1-1.5K, trying a visit to Audi to see if the system can be unlocked, no doubt this will cost a lot as well.
i will put up a new post after speaking with them, I don't understand why they would put such a poor system in a quality car like this.