Why not make a “5.1” mix and keep the rears quiet? All the sound is left, right and bass.
Why… just leave it as stereo if that is what you want. It seems the consensus of those who are most familiar with this is that either leave it as stereo or make a 5.1 mix. Anything in between is pretty pointless. I’ve taken that advice with my 77 surround mix by making the rear channels identical to match the 4.1/4.2 original, but I’m using the full 5.1 channels and not making a specific 4.1 mix which the specs say is perfectly acceptable. Oddballs like that just don’t play well on most systems.