I have noticed that the speaker fill enhancement is gone. That option was useful to play stereo sound on both front and back speakers in my 5.1 setup. It was there very recently. The closest I could find to do something similar is the surround option in sonic studio 3 but it won't work on some application, like firefox or MPC. I've tried to use the realtek drivers from the realtek site and no speaker fill either. I've read that the recent creator update for windows 10 removed that option.
This is an ongoing problem with ASUS for some unknown reason they have not enabled speaker fill on the Realtek audio codec drivers, the hardware is capable of doing it the drivers they are providing are the problem.