You are saying if you test the speakers after setting them to 5.1 the speakers will not test as 5.1?
That system has the SupremeFX8-Channel Definition Audio? My ASUS Z490 does not have that so our Realtek panels may look different. I believe we also have different drivers.
There was another thread recently with about the same situation. I do not think that was resolved.
This is my Realtek Console without SupremeFX.
What I am wondering is the FX8 is described as Channel Definition Audio. If that means it is what is turning your stereo into 5.1, possibly it is not installed or not working correctly. Do you see any evidence of the FX8 codec on your system? I might assume it should have been installed with the Realtek driver.
Again, since I don't have that system I can only guess.