PSA: Use these Audio settings.

[Shodan]

Sound Volume at half, Score Volume maxed out and Dialogue Balance at half.

At least if you find gunshots obnoxiously loud and music masked by gunshots and other noise.

I play on speakers and with the default settings, gunshots were always just too loud unlike any other game and music was completely masked by the unbearable noise from gunshots and other stuff. I would just turn down volume and then gunshots would be fine, but I still wouldn't be able to hear music at all when there's a huge shootout in a mission. Same with high volume. Either way, music is pretty much completely masked by gunshots.

When I turned down Sound Volume to half and maxed out Score Volume, it was absolutely perfect once I increased volume of my speakers enough. Gunshots were exactly as loud as I wanted them to be, no more or less than that, same with dialogue, and music was not masked by any other sounds whatsoever. Even in the most intense shootouts, music could be heard perfectly as if I was listening to the tracks alone on YouTube, but that being said, the music still didn't feel unnaturally loud compared to gunshots and dialogue and other stuff at all, it didn't stand out too much, not even close, it was all just perfectly balanced and I mean 100% perfectly once I found the right volume of the speakers after applying those audio settings.

If you had the same issue, give this a try. This game has one of the best soundtracks out of anything ever made, not just games, and it's a tragedy to be unable to hear it because of gunshots and other noise. When you can actually hear it properly, the music just makes all the brilliant scenes hit so much harder, it's just amazing.