Stereo music wasnt designed for a 3D environments, its good for 2D music (like listening to your ipod or whatever) because its not in 3D and gives the illusion of it.
The reason it cant be stereo is because it was designed for 2D music. Mono music is used because it works well in a 3D enviro, giving only 1 point of audio. In popular engines (like unity and UE4) the tracks are combined and what you hear is actually mono. Blockland doesn't do this because its not implemented (no to mention the engine is years old)
So no, you cannot use stereo tracks. Combine them or make only 1 track available.
Good for ingame music that you hear everywhere. Bad for normal sounds (ie gun shots), because it creates what we call Spatialization
Spatialization is basically making a sound feel like its to the left of you, right of you, or even above you. Creating sound in a 3D environment basically.
To summarize:
Stereo: Good for music (globally) or 2D Sounds.
Mono: Good for 3D sounds like a gun shot.
Combining both tracks automatically when creating audio datablocks would be nice.