This question is here partly because I simply don't know where else to ask it, and I have spent this whole evening on Google, and partly because MusicBee does not give me this problem, so I am hoping someone here will have an answer as to what is going on.
If I play a particular MP4 with Musicbee (ie just the music without the video) it successfully upmixes and I get sound out of all 5 speakers and the sub.
If I play the same MP4 with VLC player then I get the sound out of 5 speakers but not the sub. This happens also with other video players. I think I have tried every combination of audio setting in VLC and on my sound card. MusicBee plays correctly every time. VLC does not.
What is it that MusicBee is doing that the video players are not doing, and does anyone know of a video player which will play through all 5 speakers and the sub in the same way that MusicBee does?