I use this to create custom sounds in Modlets, but it may help you
1° You will add your sounds to Unity3D and export them as a ".unity3d" file
2° Create a "sounds.xml" file, and add it to your "Config" folder
3° The path you will use is gonna be something like this (example)
<AudioClip ClipName="#@modfolder:Resources/SOM1.2.1.unity3d?AK74"/>
Resources: The folder where your "Sounds.unity3d" will be placed
SOM1.2.1: The name of the folder in Unity that contains your sounds
AK74: Name of the file contained in "SOM1.2.1" folder in Unity
Hope i helped.