Talking to one of the more reputable 3-piece wheel mfg and they mentioned that for a A6 4.2l they would use a 19x9" wheel with +32 offset.

If my numbers are correct, it seems like the wheel will push past the fender by a good amount. Trying to size up wheels to be dead even with the fender, and I calculated a 19x9.5" +40-43 offset to be good.

Thoughts, suggestions?

rubbing. I ran 20x9 A8 replica's with a ET35 & although I didn't rub on the back tires I had occassional rubbing in the front.

Then again, you are losing 1 inch in diameter but I still think they'll be pushed to far out.

Ok, that is what I thought. I'm not sure what they are thinking. Maybe they mistook an A6 S-Line for an S6, but even at that, i don't think an S6 has wider fenders than a normal S-Line.