Garage Cabinets, Garage Storage, and Garage Organization

I bought a 2006 B200 CDI.  Love the handling, interior, looks and all.  The one thing I cannot stand is the audio system ( I am an audio freak!).  My car comes with an Audio 5 system, and would  love to replace it with a "real" audio system, but the dealer tells me that because of the fiber optics in the car, that cannot be done.

I want to put in a nice cd/dvd player, amps and sub woofers, or at least a nicer system from Mercedes.  I got a hold of an Audio 20 system (cd changer and phone hook ups included) from a wrecked 2006 SLK, but again the dealer said it could not be installed in my car, since the  dash parts and cables are not available from the factory.  Of course, they can sell me a new unit (Audio 20), with no CD changer or anything else included, for "just" US $5,000.00

To the point: where can I find original audio systems for my car, or what  systems would anybody recommend for me  to buy, including installation kits for theB200

PD: By the way, I am in Costa Rica, and the B-Class was introduced here late last year