Labelman, excuse me correcting terminology, but it will help you find the info you need.
Universal Media Interface is the old name for Navigation 20. That is a retrofit navigation and iPod system for the current shape C/E classes, before the mid 2011 updates.
Media Interface, internally known as UCI (which I think was Universal Communications Interface) is the 'advanced' iPod kit that uses the head unit for display and control of track info etc.
So you should be looking for info on UCI or Media Interface. UCI has been a factory fitted option (and retrofittable althouth Mercedes don't always agree) for most Mercedes since late 2008 (and the W204 C class from launch).
However, UCI sits on the fibre optic network, so your stereo must have a fibre optic port. In general the basic single disk Audio20 does not have a fibre optic port and thus you need at least the Audio-20 with in-built CD changer.
I hope that helps
Richard