D3 S8 buying advice

[sarg]

Now my Boxster has gone to its new carer, I am starting to shortlist my next car, at the moment it's a not a very short list but the D3 S8 is certainly on it, as well as C6 S6.

So, having not owned a D3 before, what should I be looking for?

Rear brake calipers
Suspension troubles
Electrical gremlins

Any other common gripes?

There are a couple of S8s I quite like. One is a 2007/07 basic spec with 60k miles at £17k, the other a 2008/58 facelift car with ACC and ceramics with 51k miles at £23k. Also a 2006 S6 Avant standard spec with 70k miles at £14k. Others in the running are an E60 M5, E90 335i/335d or a RRS/Touareg/Q7/X5

I know the cosmetic differences for facelift, but what else was 'improved'?

The sat nav changes to HDD based I know, but is this a dealer only option for updating, as opposed to the 'back-up' DVD updates available.

If I do buy another Audi, VCDS or similar will be an essential purchase, which is the best one to get and what else do I need to be able to read and translate codes? Anyone tried one of the Bluetooth transmitters that plugs in the port and sends the info live to your smartphone?

Ceramic brakes: I know they can be removed, sold on and replaced with standard brakes, but what is required? Is it simply reaplcement discs and pads, or do other components also need changing, such as calipers, hubs, etc?

Can't find any S8s with B&O currently (excluding the silly season priced one with Oscar Goldman - 28k) so is the Bose good enough without waiting for a B&O car?

Any suggestions for who to use for a PPI? Cras in question are in Cardiff, High Wycombe and Oxford - anyone in those areas with VCDS that could help?

Lastly, one of the negatives against another Audi is the lack of a decent local specialist - I used to use RSD in Daventry but was never overely confident in them, nor were their prices especially cheap, Revo are also in Daventry but only do performance tuning I think (?) so anyone got any other ideas in the Midlands - Ranj, Amar, Ainarss?