Hello.
I'm sorry, but near everybody has that problem, even me!
All you should know is, that you can't fix it. There is no solution since 2012.
No driver fixes, no excuses, nothing. Just blame.
Official ASUS Support always says: "We have no information about that problem, try to install new drivers."
In other words: " Just **ck you!"
I saw a lot of threads and forums, where people were mad about that. A lot of them brought the sound card back, and the others (like me and you) are switching every day between "Stereo" and "Surround" to get it working. Sad, but true. 😞
If you find a solution, I will be grateful. 😮