Late '90 - early '00 C,E,S, SL MB came with very similar radio models. On the front, they look exactly the same. I don't know any difference on the outside except functionally, some radios did not have fader control when entering "aud" settings for balance, treble, bass. On the inside, the radios must be opened to see if there's any difference.
The radio in your car may be modded. Read through here and give it a try. http://www.benzworld.org/forums/audio-telematics-forum/1663833-2002-e320-radio-question.html
If you can do it, you can play whatever gadget that has a headphone out.
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