I know there are people who think I'm crazy or biased, but having just spent a fair amount of time in a new A6 (
http://www.nextautos.com/buyers-guide-2009-audi-a6-30t-quattro and no I didn't write the review) I prefer the new SHO to just about everything over the Audi, including interior, fit/finish, straight-line and cornering performance. If anything the SHO is even quieter than the Audi, (which is actually one of the few things I prefer over the SHO, though I think having that quiet of a car says a LOT about the quality of this new SHO when compared to the German competition.) And the SHO does it for a lot less.
That said, the Audi has more legroom in the back, and I like the overall styling a bit better. Less chunky looking.
I know there are a ton of people who can't fathom a domestic manufacturer building a car that competes with upscale Germans, but to the non-believers, let me just say this again: See this car in person and drive it. You'll be quite surprised at what you find.