Need info about replacing stereo system

I am about to replace the cassette player on my 1994 C280 with an Alpine or JVC CD player. Has anyone encountered any problems with such a change?

I have been told by the installer that they might have to rewire or circumvent the built in amplifier that operates with the cassette player when the CD player is installed. I was told that they might have to rewire the ignition switch or I may only be able to listen to the stereo while driving. What gives? Are M-B's that problematic when changing anything from what was installed at the factory?

Thanks,

i plan to do the same on my 94 c280.. i just bought a jvc combo head/ changer unit. how did yours go?