Revised to correct VMS/IP
Possibility that your TV does not support Dolby Digital. If so the STB must be changed to output PCM only.
Settings on newer (VMS and IP) boxes, press and hold D button for about 10 seconds and hidden menu is Displayed. Navigate to user settings, HDMI additional settings. left or right to change setting to L-PCM
For older boxes (at least the 7xxx and 6xxx) you need to reach the hidden menus
- From on, power off just the STB. Usually best to do this at the STB as you want the TV to remain on.
- Hit OK on the remote
- Hit Menu on the remote
- Head to the HDMI menu and set L-PCM
Note this is all timing dependent so you may have to try a few times. Note if you hit OK in the third step a different hidden diagnostic menu shows up.
I never had the CISCO boxes. I think someone said you could reach the settings from the regular menus, but not positive.