Thanks Rudney, yep I do have the manual and it seems my problem is deeper that that. There is simply no AUx option under audio. I have a friend with the identical car, 2010 SL and it also has no aux. Really strange since my CLK 2008 model has no problems.. Thanks again
If you have connected a 3.5mm jack input to your AUX on your Comand it should come up on the display and like wise if you do not connect then it wont show. For example I have Radio, Bluetooth Streaming CD, AUX etc. Now my car did not have AUX originally but I have an adaptor installed that gives me Bluetooth Streaming, USB and AUX, when I attach the AUX input it then shows AUX on my Comand, I can also have USB and / or Digital Radio but it is all through the AUX.
Now you could try pressing the number '6' or right arrow to see if AUX shows by cycing through, this is how I use mine?
Also it may be worth taking out your Comand and seeing if the AUX input is plugged in.
You can use this video of mine to help you remove: