Hi Luke,
I went from owning 4 Skoda Superbs (MkIIs and then MkIIIs) into an A6 like yours. I found myself getting numbness under my thighs, and I was concerned in case it would turn out to be a showstopper. In my case, the solution was to have the seat much lower than I was previously used to. Once I'd reached that level of adjustment, I've had no further comfort issues. If you haven't tried this, it might be worth a go. Not suggesting for a moment this will resolve it for you or anyone else, it's just my experience.
Have you tried also adjusting the lumbar support? I set that to the point where I could only just detect the pressure from it and no further.
You might also try going on the motorway (If you can get to one quickly from starting a drive) and seeing if the problem is less after a period driving with the cruise control only - so you have minimum pedal usage (easier if you have adaptive cruise control).
The only other thought is perhaps to go for a test drive in another identical model via the dealership in case there's something faulty about your specific driver's seat...
Good luck!