Use real "upmixing" algorithm
In #496 and #461 (comment 752873) I already expressed that copying stereo channels is as stupid as flat Earth conspiracy theories because directional information does not magically materialize from the cosmic ether.
However, for more than a decade there were a research paper floating around on that topic which you can find in pdf form. It describes several "proper" algorithms among which "Passive Surround Decoding" and "Adaptive Panning Method" seems to be most performant. Although any such method merely simulates echo propagation in a virtual room and does not substitute to properly mastered surround recordings because nothing does.
If you're going to enable such things by default, please, at least use a real algorithm.
Maybe you can even find something more advanced that was made in the last 10 years.