I need to install an aftermarket navigation system in a 2003 C240. It has a factory CD changer in the glove box, 4 door speakers with tweeters in front, and a factory 8" sub in the rear deck. I've pulled the radio and it appears to have a standard VW harness and antenna, and a 2 pin fiber optic harness. It looks to me like the fiber optic cables are only for the CD changer, but I am not certain. I found an antenna adapter, dash kit, and wiring harness available from Metra, but the Metra tech says I need to rewire each speaker if the car has a factory amplifier. Has anyone attempted an install like this? Modifying the dash kit or running wires is no problem, but I need to know what all is involved with this install before I jump in. If the factory radio is replaced, will it cause any problems with the cars computer system? Will the factory amplifier still be functional? Any information would be greatly appreciated!