Surround sound issue with some HD channels - DirecTV

Motorola receiver is not receiving 5.1 surround sound on some HD channels. Receiver is connected to LG BH6820SW home theater via optical cable. Have gone through complete u-verse troubleshooting/restarting, etc. with no success restoring 5.1 sound to channels affected. Surround sound is fine when using DVDs and on some HD channnels. Anybody have a clue what's going on? THANKS!!!

This question, "Surround sound issue with some HD channels," is about DirecTV channels, programming, equipment, and sports.