Question Help getting surround sound from Xonar DGX optical out


Dec 12, 2008
I'm trying to connect my PC to a Yamaha RX675 receiver through an optical out on the Xonar DGX to get 5.1 surround. I'm aware that DGX can't encode on the fly so I'm not looking to get surround in games or Windows, just when playing already encoded DTS/Dolby 5.1 streams in movies and such. From what I read DGX is capable in passing a pre-encoded stream without problems, but so far I've had no luck getting it to work.

This is how I have it set up at the moment:
Default output device in Windows Sound Control Panel is set to "Realtek Speakers"

The configuration of that device is set to output 5.1 surround.

In the Realtek software I have SPDIF output checked and it's set to PCM mode (the only mode it has available).

My reciever is set to "straight" mode meaning it should just decode any signal as is.

All the sources I've tried were from digital-theaters website meant as test files for surround systems and I played them through VLC.

I've tried various settings in VLC, tried setting the SPDIF passthrough to "Enable" tried "DTS/DD only" but nothing works.

All the audio is played only from two channels (front L/R). My reciever screen is showing "PCM" on its display and only has two channels lit up. No matter what source I play it from.

I'm suspecting that because I have PCM selected in the Realtek software as the mode that it's not even passing the DTS encoded signal and just converts everything to 2 chanel PCM, but the thing is that there is no other mode available. As soon as I check mark "SPDIF out" PCM mode just becomes active by default with no option to change it to anything else.

Does anyone know what could be the issue? Thanks.