All the examples are "almost valid" turtle (apart form the "instrument:" namespace).
Check also OntologyCompatibilityLayer, to see the axioms allowing to reach this expressiveness, bridging the gap between these
two ontologies.
There is also, here, the email on the Music Ontology mailing list summarizing the thoughts I am trying to make more concrete here.
And finally, here are the currently identified issues: OntologyOpenIssues.
-- YvesRaimond - 13 Feb 2007