The turbo 3.0T takes well to tuning (stage tunes, and on built cars larger turbos and ethanol flashes add big power), so a meaningful share of B9s on the market are modified. Confirm exactly what's been done and whether the ECU/TCU are stock if you want a factory car or a documented build.
Responds well to a tune; check stock vs. modified
Audi S4 (B9) · drivetrain