Part of that difference can be attributed to the seven speed dual clutch gearbox in the Audi versus an 8-speed automatic in the BMW. The Audi is fairly heavier though with a weight of 3953 pounds to the BMW's 3719 pounds. Finally a new BMW that is actually lighter than the comparable Audi although the new B9 is coming which promises to be much lighter. Unfortunately handling performance was not measured.
Regardless, Auto Motor Und Sport does state in their impressions the handling of the Audi was better and more responsive. Ultimately it was a close battle with the S4 coming out on top due to the handling, engine, and transmission. Chalk up another BMW loss.