I have the full 3D burmester system in my S63. It's not nearly as good as I thought it would be, but not bad. I like the extra lights in the tweeter and speakers, which is why I wanted it, plus it's definitely good. Having said that, I think any competent stereo shop can install a system that sound as good as the Burmester 3D setup for around the same price as the facotry 3D system, $6K USD. The above the head speaker locations are great - and in my opinion, the best part of the system. The main door speakers are nice, as are the rotating tweeters, but the speaker location on the lower part of the door panels aren't the best, since they're next to and below the seat cushions. A custom fabricated speaker pod that isn't blocked by a seat would perform better, provided the equipment is of good quality. You might even place tweeters in the B-pillars. Also, have them design and build a custom subwoofer enclosure, then open a passage from the trunk to the passenger compartment for the bass to travel through. The most important thing is the sound processing, in this situation a good sound processor has the ability to improve sound quality dramatically. The big advantage to adding sound to an S-class is how quiet the car is. You don't need high powered amplifiers to overcome road noise. A cohesive design and implementation will give you more bang than high end components that don't play nicely together.
I'm a former car audio guy, not so much anymore. But I have an 11.4 Dolby Atmos system in my home theater, nothing in car can come close to that.