Plex Web trying to play 5.1?

I user is reporting to me that their sound is messed up, sounds like the person is really far away while other effects are very loud. Sounds to me like it’s trying to play 5.1 (Which is what all my files are pretty much). I checked PlexPi history and checked the stream, and it was indeed trying to send him 5.1, but the strange thing is, he is on chrome. I thought to browsers it was automatically converted to mp3?
Anyway, what can I do to force it to 2 channels?

Thanks!

Correction. He is on a Mac and is using safari. Not sure if that makes a difference.