I'm trying to figure out what I have to do to enable the "CH-IN" as an aux input to the head unit. I only have two options for sources on the screen (radio and CD) but I would expect to see a third. I tried switching while I sent sound through the RCA cable (in the back of the unit), but it still didn't let me switch. It's like Panasonic locked things where you could only use the input for a CD changer or an XM radio and nothing else. What do I have to do to make the player switch to this input without one of these special devices?