If you are having trouble setting up your Zvox AV120 you may need to make a few changes in your TV settings.  

The TV's internal speakers should be turned off and the audio output format should be changed to PCM.  The below videos will go into greater detail on how to make these changes.  

The video below shows the AV100 but it also applies to the AV120.

AV100/AV120 Optical Connection and Settings Shown on a Samsung TV