I saw the Wiki, it stated that custom sounds are in later versions, and are broken. Is there any version of minecraft that chance cubes support custom sounds?

Ahhh, my bad. I believe it does work now and I simply forgot to remove that disclaimer. Let me know if it doesn't work though.

I am using the 1.10.2 version, surprisingly it doesn't work at all, the one I used is the latest version with the fixed relativetoplayer, compiled through gradlew. I don't know if it only applies to me. Hope you can try testing it with your own custom sounds on 1.10.2 version.