If you're thinking about getting different speakers, you'll need to completely re-wire the system and put in a different amp = Big $$$
IMHO, the best solution is a direct replacement. Bose systems are excellent and the replacement speakers directly from Bose are approx $50. When you think about it, 11 years on a speaker in cars is pretty darn good. Bumps in the road, moisture, loud volumes, etc all take their toll. See this thread:
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!