You should not use the EU update. What source are you using to see updates? I believe that you should be able to use the updates located on the FutabaUSA site.
2.7.3 is the current 18MZ version and 3.11 is the current 18SZ version
Not sure if there is region coding as in earlier models, but I do know the EU has new rules regarding protocols, etc. Those do not apply to Australia as far as I know.