Well, actually I think they went down a bad road with the music files considering they wanted to make the game moddable and the editor accessible to the broad public. It is a good choice, probably even the best one for game designers and hobby modders. But it is not easily accessible, here is why:
The sound files used are called wwise soundbanks or short "*.bnk" . Wwise is a programm by Audiokinetic and is a professional tool for creating soundeffects and music for cross-platform games. This means it is a very powerful tool, espc. with its SDKs and addons. However, this means also it is fairly complex and "just converting a *.wav or even *.mp3 to *.bnk" is NOT possible (mp3 not supported, but that there are good reasons for that). The reason is the way a *.bnk sound file saves information about various effects and not just the audio part, so it is easily used inside an editor.
Information about Wwise:
https://www.audiokinetic.com/products/wwise/FREE license (slow) download:
https://www.audiokinetic.com/downloads/If you want to get into creating *.bnk files check the TUTORIALS on Wwise:
https://www.audiokinetic.com/resources/videos/Regards,
Chris
