Rear speaker audio is too quiet when playing 5.1 audio on a stereo setup. Any way to change this?

I've noticed while editing video game footage with 5.1 sound, that characters speaking in the rear speakers are very quiet when I'm editing with headphones, but when I export the video, everything sounds perfectly clear when I play the video back in various media player apps (as well as when I listen on 5.1 speakers)

It seems that Premiere is decreasing the volume of the rear speakers when downmixing for stereo playback, but I can't seem to find any way modify the way this downmix works. I don't actually want to modify the rear channels, because like I said, when exported, everything sounds fine. I just want to modify the way it sounds when I play it back in the editor, while using a stereo output device.

I'm typing subtitles for this footage, so it can be frustrating when I can't hear dialogue from the rear speakers very clearly.