Usually when I am playing a campaign mission (I play with classic music btw) The cutscene and In game sound effects overpower the dialog.
Example.
Main theme music: BA DA BUM BA DA!
Chief:We need to activate Halo’s defenses
Me: I can’t hear you
Anybody else having this problem?
Yeah same here. I have play with the volume up high most of the time so I can hear what people are saying during cutscenes.
Yeah, I needed to turn subtitles on. It was louder in the original game. I don’t see why there isn’t an option to set the volumes to how you want. Halo PC has it.
Yes, I agree that this is a problem sometimes. I really wish there was a separate audio menu to adjust different audio levels. I also wish you could switch between classic and remastered sound effects…that would be awesome. Whenever I’m in that classic mood, not being able to use the classic sound effects kinda bugs me sometimes. And I know I can put in the original game, but even the classic mode has been given a clearer HD makeover in anniversary. I think it’s the only thing missing from making it a truly complete package.
This has ALWAYS been a problem with bungie games. There is still dialogue from halo 2 and 3 that i dont know what they said.
I think that the audio is mixed optimally for 5.1, and when your not using that center speech channel it gets mashed in with the music.
This is strange, I have the complete opposite problem. When I play the game I can barely hear the music, while all the sound effects and dialogue massively overpower it.
It’s a shame really, I absolutely love the remastered music, particularly the AotCR stuff, but I can never hear it because between dialogue between members of the Covenant, the snow sound effects and the sound of me firing weapons, I can never hear the damn stuff 
I think it’s fine.
I dont have this problem its sounds strange it could be you glitching the game becuase on some cut sceens there isnt sapossed to be music but you can glitch it by getting to the point where you see the cutsceen before the music is over so it plays through the cutsceen
I agree. When I’m playing the game at a perfect volume, the cutscene dialogue is much quieter. Especially comparable when you hear Cortana talking in game, then hear her talking in the cutscene.