Well now...just got my Stebro final mufflers for A6 4.2L... won't post total opinion yet, but..stock sized piping is a minus. Non-mandrel bends is a minus. Countering that, they are reasonably light, and the design on the interior of the mufflers looks very solid. Tips are single-wall, and the 'large' is only 3" which isn't going to give anyone tip-envy :-)
So, we'll see. The non-mandrel bends are dubious in terms of the area for flow at the curves...but I'm certain the mufflers are much less restrictive...and all of that doesn't matter much anyway because restrictions at teh headers, precats and cats probably render it almost-moot.
Worth noting that they offer club discounts.
More to follow after install.