No dialogue audio in 5.1/Bitstream

I have a marantz 1403 receiver and 5.1 speakers. In Halo MCC, when audio is set to 5.1 or bitsteam in the xbox one settings, dialogue (perhaps centre channel?) audio is so low voices can’t be heard during cutscenes. Other games function fine with these settings.
Setting Audio to Stereo is not a fix for this issue, I’d like to play the game with 5.1 audio.
Can this bug please be addressed?

Thanks!

Yes, this bug really needs addressing. None of my other games have this issue, nor my ps4, Chromecast, amazon fire TV or other devices. Please fix.