Try setting the speakers to "NO EFFECT" or taking it out of the 3D audio you spoke of... If this has no effect, and I did not ask this earlier... is the stereo sound in ALL playback events or only with music/video.
Reason asking, is:
- Soundtracks in games allows for manual setting to match your speaker configuration
- Some music player programs allow for manual setting for decoding to allow for multi-speaker setups (on PC)
On another note I found this which may explain a lot even though the user is using a GA-Z170X-Gaming 7-EU (rev. 1.0). This is from: https://hardforum.com/threads/gigabyte-z170x-gaming-7-lga-1151-motherboard-review-h.1876576/:
I've got a vanilla optical cable (which basically needs to transfer light from one end to the other). there IS SOUND via the receiver, but it's only stereo (so the cable's not the culprit). my receiver can detect when dolby/DTS is present. not the case with this mobo.
I've tries almost everything I can think of (and that I know worked for me in the past), but nothing's working...
I'm in contact with Gigabyte at the moment, and what they're saing is this:
"Please understand that different product may design with different features. GA-Z170X-Gaming 7-EU (rev. 1.0) had confirmed released without Dolby / DTS features, if you need the function of S/PDIF 5.1 channel, you need to purchase the motherboard with the license support of Dolby / DTS; otherwise, you need to purchase the license from vendor directly or other hardware / software solutions. Sorry for the inconvenience."
So I suggest that you double check if your system is really outputting 5.1 audio... right now' I am very pissed at Gigabyte!!! it took them three replies to tell me that the s/pdif doesn't support dolby/DTS, and thus far hasn't given me any meaningful help or solution
Even though you are connecting direct to your Logitech Z's, this MAY apply to your motherboard sound-chip as well. This would explain why your X-Box could/can decode no problem. IF so, your only other option is to use analog connections OR go with an add-on soundcard that offers DTS/Dolby encoding.
Honestly, you'll have a hard time telling the difference between optical and analog with plug-n-play speakers, if you go the analog route.
Hope this helps/sheds some light on your situation...