Audi S4
Audi's quattro four-wheel-drive system was standard on the C4 S4/S6; a first-generation Torsen-based system which used the "T-1" automatically biasing centre differential (ATB) was used on vehicles equipped with manual transmissions, while a transfer box based system was used on vehicles equipped with an automatic transmission.
Audi S6
The S6, like all Audi "S" models, is fitted as standard with Audi's trademark quattro four-wheel drive (4WD) system, the S6 using the Torsen-based permanent 4WD.