I have a Panasonic Viera plasma with a headphone jack in the side panel. When I plug in my regular 3.5mm headphones, the sound stays coming through the TV speakers with no sound through the headphones. I looked in the user manual and it says something along the lines of the TV has a M3 stereo mini plug socket. What the hell is that and why does the 3.5mm jack seem to fit perfectly? Any info would be appreciated.