Not sure about your model, but it may be necessary to turn the external speakers ON in the Audio menu settings.
I am trying to hook up my very old bose system (Bose Lifestyle 8 Series I System) to this TV. As of now, I have a Dish Network receiver hooked into the TV via AVI cables, a 3D Blu Ray player via HDMI, and a PS3 via HDMI.
As for the Bose system, I have the surround sound speakers hooked into the "Music Center," which is basically the unit that selects AUX, Video, CD, etc. From the Music Center, I run a black and red RCA cable from the "Video" jacks into the back of the TV.
After trying to watch TV with the dish, and muting the internal speakers, there is no sound. I believe we had a similar or exact setup on our previous TV (a Visio plasma) and it worked fine.
If possible I would like to be able to use the external speakers for the dish, bluray player, and ps3.
Am I doing something wrong or is the sound system just too old? Help appreciated thanks