RS 6 typ 4f (C6 4F) wagon?
5.0 V10
Yessss ... ding ding, we have a winner ... ah wait... is not called wagon ... is called "Avant"

The engine is from Lamborghini Gallardo (VAG owns Lamborghini), many parts still have lamborghini stamp on them but Audi added 2 turbos to be more appropriate for a large and heavy family wagon for their RS line up.
The factory declared is 580hp and 650 N⋅m (479 lbf⋅ft) of torque from 1,500 to 6,250 rpm, but in reality seems like the power is about 610hp, hence the 100-120hp gains from only a tune.
In RS line up the V8 or V6 is standard engine for Audi, they tried only this model with V10 twin turbo but the time frame was very bad (financial crisis 2008-2010) and they switched back to V8 afterwards.
More info:
https://en.wikipedia.org/wiki/Audi_RS_6#C6_(Typ_4F,_2008%E2%80%932010)Yep, shows how much I don't follow any VW-related brands anymore...even Porsche gets a yawn from me these days.
Not a problem, if you got something from this topic than is a gain, any gain is good. We can't keep up with everything or our heads will explode.