I'm just guessing, but I would assume the stock unit has the amp integrated. In '96 Mercedes went to the Bose 8 speaker 200Watt system. Can you check your owners manual or call Mercedes for the power output of the stock deck? Aftermarket decks such as my Pioneer deliver 22W RMS/50W peak to each speaker. Pioneer also uses the MOSFET amp which is supposedly a decent built-in amp.

The good news is (hopefully) that the absence of a fader switch means an easier install if you choose to do it yourself. My brother and I did both the receiver swap as well as rewiring from the spiderweb of wires the previous installer crammed behind my dash (had an older Alpine system I was replacing).

Anyway, find the power on your stock deck, and that will go a ways towards answering your question.