From my searching, Speaker Fill is, at best, brokenand that's when using standard sound outputs.
The general consensus seems to be to roll back the High Definition Audio driver to the "02/27/2017" version, reconfigure Playback Devices, and select Speaker Fill in Enhancements under Speaker Properties.
Reboot the machine and, if it works, you're one of the lucky ones. If it doesn't, look for something other than Speaker Fill.
There are lots of "Good luck. Glad it's not me" sorts of wrap-ups on that one, so you may be on a mission to find the pot of gold at the end of the rainbow, on this one.
Since I only use Linux, I can't offer better than that, at this time. Hopefully somebody else will have a proven method that applies to your specific situation, if the above doesn't work for you.