2004 S500 4matic without brembo front brakes
FWD and AWD cars tend to have less front scrub radius than RWD cars, to minimise torque steer. This tends to push the brakes outboard, leaving no room for 4 piston calipers.
Nick
Mercedes > 2004 > S500 > 4Matic > Brakes
and came up with this picture. Do your brakes look like this:






