No digital audio output through optical

I have a 5.1 sound system that only has 6ch input and stereo input (left/right composite). I don’t use the stereo input. The 6ch input is connected to the 6ch output of a USB External 7.1 Channel Audio adapter.

The USB External 7.1 Channel Audio adapter has an optical input and a 3.5mm line input. If I plug a 3.5mm cable from the AV out to the Line-In I get a horrible buzz (my friend said this is because the AV out is supposed to be plugged into a 3.5mm jack with a red/white/yellow composite on the other end; I’ve never seen any such thing so I’m questioning this) but the sound is there. If I plug the optical output into the SPDIF input of the USB External 7.1 Channel Audio adapter I get no sound.

I’ve changed the Audio/Video Input/Output settings in my WD Live TV to Digital Pass-Through via Optical only and selected DTS and dolby support for my sound system.

I’ve also double-checked to make sure the USB External 7.1 Channel Audio adapter has its SPDIF input enabled. It is of course plugged into a computer to configure the adapter.

i updated to the latest firmware version 1.13.18

I’m really trying to figure out any way to connect the Live TV to my sound system, but as near as I can tell trying to use the optical through the 7.1 Channel Audio adapter is the only way I can get an input from the Live TV to the sound system.

Thanks for your help.

Composite cables will only get you stereo sound. Check if the adapter that you are using supports DTS audio. 

I don’t want to use the stereo sound because that is a waste of my surround sound system. Is there any use for the AV out of the WD LiveTV?

And I’ve been going back and forth with support from the 7.1 Audio adapter and checked that all four options should be enabled in my digital optical pass-through. I’ve tried them all individually, all at once and in several different combos (wma pro, dts, dolby,acc, etc.)