In Godot you can code in audio controls (audiostreamplayer) along with using audio buses to put them into different channels. IE if you had a bunch of stuff on iphone, you could set that to one bus and then control all the iphone volumes.
It's not super straight forward but it works well. I basically created a bunch of const then a function that linked everything together to control the paths and the volume. Then when I needed whale music, I could just call the whale music. The player could also control the volume of said music on the menu slider while allowing me to equalize things individually.