I have that exact setup in my 91 300E. The head unit is a breeze to wire in. Just like a normal radio. You will only need the fiberoptics if you choose to integrate the 6disc or the Startac setup. I mounted my changer in the glovey and ran a 1.5' of fiberoptic from the headunit to changer. The only drawback was that I was lazy. My car has the Active Bass system stock and I just bypassed the two amps in the trunk and ran the speakers straight to the HU. Definitely not as loud, but we can take care of that . A friend has the whole setup in his 90 124 diesel, startac and all

Bill
1991 300E