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 S4
Bose sound system is now standard, whereas it was optional on the B6 S4, and an enhanced optional DVD-ROM-based RNS-E satellite navigation system replaces the previous CD-ROM-based RNS-D option.