i just registered to give you the following link:
[url=http://www.microsoft...sid=Windows 8.1]Microsoft Support Forum[/url]
I have the same problem and this worked for me. Good luck!
Just in case the link doesn't work in the future, here is what it says:
After my Win8.1 update, everything that was working on Win8 is fine with the exception of my audio drivers. In short, every time Windows restarts, my drivers/sound settings revert to default settings and I get no sound.
If I go into the Console Launcher and change my mode from Game to Audio Creation, suddenly everything 'kicks in' and begins working, normal sound, etc. But my settings are all at default and I have to reconfigure them (for example, change the flexi-jack from line-in to microphone so that I can use my headset microphone, and change speakers from 2.1 to 7.1). No further issues while I'm using the system at that point. But once Windows restarts, sound no longer works and everything is back to default. Change the mode, and I'm back in business but need to reconfigure everything again.