5.1 audio

Hope someone can help me out i own 2 roamios both my tivos do the same thing when i use my optical port from romio to my sound bar on 1 channel NBC HD on cox cable sounds like mono channel sound i have dolby audio checked i have tried everything all my other channels are perfectly fine PCM fixes this issue but 2 channel audio is a joke i have a 5.1 system and like said all my other channels are fine on dolby audio please any help would be great thanks.

5.1 audio