New LG55LA7400 and Panasonic SC-BHT20 home theater unit. Using HDMI ARC out on the speakers connected to HDMI ARC on the TV. TV setting - external speakers HDMI ARC/digital optical cable. No sound. I've also tried using a digital optical cable with no success. My TV input is over-the-air. Any suggestions?
It seems as though you have the connections correct. You certainly should get audio over optical even if there is some issue going on with the ARC function. Try disconnecting the ARC and just using optical and be sure you're selecting the correct input on the soundbar.