We have a 2011 GL450 with the Rear Entertainment System. I have a video source plugged into the rear disk aux inputs (the RCA plugs in the center - not in the monitor). Is there any way for me to have the audio from that input play through the speakers? I've read the manual and thought I saw some indication that it was possible, but I haven't been able to make it happen. Is what I'm trying to do possible?

I also have the same issue with my 2011 GL550 where my disc is playing from the rear but cannot get audio through speakers only on headset... any ideas?

I know this is old, did you ever solve this?