That's pretty much where I am at now. But the only real difference between a 5.1 mix and stereo mix with only 2 source channels of audio would be more music in the back right? I'm pretty new to 5.1 mixes but from what I've read (from Izotopes guide to converting stereo to 5.1) you want dialogue front center, foley/sound fx mainly front L/R with some in the back L/R, ambience in the back, and music 75% in the front L/R and 25% in the back. If all I have is dialogue and music to work with that would basically mean dialogue in the front and a little music in the back. I don't see how that would sound much better than a solid balanced stereo mix because most 5.1 systems still play a stereo mix out of all of the speakers. Unless you just don't want that much audio coming from behind the audience. Some stuff I mix is being submitted to festivals so there is a good chance it will be screened in actual theaters.
Izotope guide for reference (number 6): https://www.izotope.com/en/blog/mixing/6-tips-for-mixing-in-surround.html