I am streaming 5.1 surround files to my Sony (x900F 2018 Model) using the Mezzmo app and have some questions about the 5.1 signal. If I send the surround audio from the TV to my receiver when streaming a video with Mezzmo using the inbuilt video player, it sends the full 5.1 surround signal to my receiver. (It also does this for any other app - Netflix, Stan, etc.)

However, if I use any other video player with Mezzmo (Mezzmo player, MX player, VLC) it down-mixes the signal to stereo. Is there any setting that I'm missing which is causing these players to not output 5.1?