So, according the the decree Sandy posted above, all the great Masses by Mozart, Haydn, Beethoven and the other giant composers are off-limits, because they're written to be accompanied by "secular" instruments; those "noisy, frivolous" things.
Please don't let this turn into an argument about religion or anything else, but I wonder how much resistance his late Holiness received from this declaration, especially from churches which were not wealthy enough to possess an organ or were located in countries with their own non-European instruments. Hmmm...