It's correct place my broadcastkey at url:
http://interactivesolution.fabbricadigitale.it/broadcastkey.mtx and in my html page used this code:
new MTSPlugin("china.mtz", 400, 400, "http://interactivesolution.fabbricadigitale.it/broadcastkey.mtx", alt, etc. etc.

Thank you
Matteo

Yes. This appears to be correct implementation.
--ED--