Godot Audio Buses and FMod

[mega-mojo]

So I'm working on a game where the developer has already implemented SFX using Godot's native audio features, and has created buses for SFX and music within Godot. I'm now plugging FMod into the project for the music, but I'm not sure how to feed the audio output from FMod into Godot's audio buses. Any ideas?

EDIT: for more context, I've seen that the developer is using the Godot Modular Settings Menu addon for the UI sliders for audio - this one: https://github.com/MarkVelez/godot-modular-settings-menu

I tried going in and editing this script but I'm still not sure what I'm doing and how to link this to the FMod stuff
addons/modular-settings-menu/scripts/settings-elements-scripts/audio_setting.gd