You can’t, it doesn’t make sense for a stereo sound to be spatialized, in real life sources of sound are mono, the spatialization effect comes from the difference in volume in each ear, since stereo already has a channel for each ear, it can’t work.
I could be wrong on this, but I would imagine most sound in games should be mono apart from music, UI sounds, ambient sounds, and cutscene specific sounds. (edit: at least for a 3D game)