I remember one of the original developers explaining in a blog post that MMX support came right before the original release and was added just for Dolby Surround, unfortunately can't find it anywhere.

The remaining references available regarding this factoid are incredibly ancient, too:

- https://groups.google.com/g/comp.sys.ibm.pc.games.misc/c/MRF...

- https://www.mobygames.com/game/644/pod/user-review/2384353/

No idea if any additional support was added in one of the subsequent releases.