Audio Systems: MB S550 4Matic, mercedes benz s550, harmon kardon

Question
I am about to buy a mercedes benz S550 4Matic and I would like to improve upon the factory installed system (500 watt Bose or Harmon Kardon) but the Bang Olufsen (1200 watts) come with a $6,000 price tag.  Is it possible to substantially improve the stereo system with an after-market solution at a much lower price tag?  Thanks for the adivce.

Answer
to be honest we have not seen many of s550, this in the shop so i have no ideas how to upgrade the sound system,
i can tell you that  $4k will buy you a nice navigation system with 5.1 sound speakers amplifiers and maybe a single woofer,

the Bang Olufsen is way to expensive

good luck