Source ETKA:
S6/S7:
Engine code: CEUC
Production: 2/2012
Power: 420HP
Capacity: 4.0
http://www.audiklub.org/silniki/-/al...di_s7/all.html

S8:
Engine code: CGTA
Production 2/2012
Power: 518
Capacity: 4.0
http://www.audiklub.org/silniki/-/al...di_s8/all.html

Here is full table (updated quite regulary), except fuel type, with is more like a guess
http://www.audiklub.org/silniki.html