The problem I am having with all this is the suggestion that anyone is being excluded from the mass. I have attended many a Catholic mass over the years, and have never been "excluded" in any way. I fully understand that if I am in a Catholic mass, I do as the Catholics do, or in a Jewish synagogue I do as the Jews do, or in a Buddhist temple, I do as the Buddhists do, or in a Protestant service, I do as the Protestants do.
To suggest that anyone is excluded from a Catholic mass is preposterously disingenuous. This has "dual tradition" Protestant sectarianism writ large all over it.
As many have suggested, you may have what in the States is commonly referred to nowadays as an ecumenical service instead of the mass. I would suggest you could also have an ecumenical mass. But none of that will appease sectarian Protestants who insist they are being "excluded" over the communion issue. No one is ever excluded from a Catholic mass, that is just Protestant superstitious mythologizing. I am reminded of my Lutheran granny saying that Lutherans weren't allowed to touch a Catholic rosary. It seems to me, many a Protestant needs to attend a Catholic mass, just to educate themselves about it.
I have no idea how many Protestants you think will not attend your events if they can't have their own service, or if the Catholics are forbidden to hold mass. It seems to me this is a ridiculous manipulation of the organization, based upon someone's anti-Catholic sentiments. Why else would this be an issue? Have you had Jews and Buddhists complaining about feeling excluded from the fleadh because of the mass? In my view, if Protestants want a traditional music organization to serve their religious worldview, nothing is stopping them from founding their own immigrant music organization and do it their way, rather than taking over someone else's. That way, at least they would leave these members, many of whom have put a lifetime of effort into this organization, in peace to enjoy the music and their mass.
I can't imagine this same suggestion being made about klezmer music.