From a 79k '03 S55 AMG.

The difference between the 00-06 years appears to only be that the '00-03 had the rear deck speakers mounted separately from the subwoofer 'enclosure', '04-06 incorporated them in it, and '03 was a transition year with speaker mounts molded into the subwoofer enclosure. This being '03, it leaves you with the option of any year '00-06 install.