For the love of all that is holy, I have tried and tried to figure out how to fix this issue. I no longer know where to turn to so I figured I'd ask on here, where maybe I can find someone who can shed some light on this issue.
Basically Windows gets borderline unstable with Optical Audio.. it's usually fine for hours, days, weeks.. months..... unless.. unless you make the mistake of hitting "Mute".. windows will mute it, and unmute, if you unmute the master it'll only unmute half of everything, it'll start erratically muting and unmuting applications and go completely nuts. I have no idea how to fix this situation, it drives me nuts. Once aggravated the issue can go on for days.. after some hours it might settle down but it becomes hard to fix.
You can change devices, plug in different devices and go back to optical, restart windows sometimes, delete and reinstall drivers. IT'LL STILL DO IT... it's awful..