this kind of ruins the whole thing, the music is way too loud, i can't lower it without lowering everything

i'm assuming it's because you put the music into "ambience" instead of "music" in each biomes file

Just wanted to let you know as I had the same issue; The music is actually connected to the Jukebox slider!
This doesn't fix the issue, but with this knowledge you can keep your normal minecraft music while silencing the sonicraft stuff.

Not sure if this is 100% connected to ops issue, but I'll add in in anyway...
I have issues with with sonicrafts music as well. It seems to play at random intervals often cutting off before finishing the track or playing multiple times and it's a bit jarring.

I have the same issue as Holo-Fox, but it only seems to happen on a server. In single-player it was fine, but on a server it just randomly starts and stops for no reason, in the overworld.