I am happy to have indirectly contributed to this. Alcaro, you can use thisthis
to make tracks.
Also, there's no real need to check for MSU1 availability unless you'll do fallback SPC music. If it's not available, sending "play track" commands will effectively do nothing, and the busy loop will terminate immediately because it'll never be nonzero.
It's the data track that causes the bigger compatibility problems and requires
an error message.