Aren't diesels, in general, taxed less? I know the US and Europe have different models, but I was under the impression diesel was always better than gas when it came to saving money, either at the pump or through taxes.
I don't care for Audi, but many magazines have rated the S6 over the new M5 and E63 because of its value. It's performance is on par with the latter two but they specifically mentioned the interior of the Audi being superior in every way. This was in C&D, July 2012.
We are talking about different models here, but I imagine the interior is similar to the S6, and therefore much better than its competitors. Or at least some quality stuff.