You could change the MB/Alpine cassette deck witih a Becker Audio 10 single disk cd player. The Audio 10 is an option in most places outside of North America. They can be purchased on the German ebay site or from www.autoclass.net It takes an experienced tech about 10 minutes to do the swap. You can do it yourself. Instructions have been posted on other forums.
Now to answer the question "is possible to add another stereo Head unit to the existing factory radio in a 2003 C230 Sedan? Yes, but it is not easy. The MB/Alpine headunit does not have any inputs or outputs. The new unit would have to be connected using an RF modulator. And the installation would look like crap in most cases.
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