I have been very fortunate to have spoken to an Audi technician yesterday (friend of a friend). After explaining the issues fully, he thinks it is highly unlikely to be a battery issue and almost definitely a problem with one of the many MMI modules. Apparently these work in a loop so an issue with one, can cause the others to stop working properly hence the additional problems I am seeing. Because the first issue was lack of sound, the first thing that would need to be investigated would be the amp and they'd go from there.
As mentioned earlier, car booked in on 24th so I'll keep this thread updated with the cause and what I eventually have to folk out to get it sorted. Fingers crossed I can afford to visit the pub again this year!!!
Andy