I only have some general knowledge but my understanding is that Gregorian Monks have been around since the middle ages doing their very deep ... very gothic chanting male voice thing.

I have loved Gregorian Chant music since I was a kid... though I don't own any... I've always wanted some.

I don't know if there is a particular music group that you may have heard that is calling themselves 'Gregorian'. Or if you heard real Monks from the Gregorian Order doing their thing.

I know that a few Goth rock bands have used Gregorian stuff as background to some of their work... Enigma being a classic example... she has some great goth/gregorian if you like that kind of thing... which I do.

Well that's all I got.
Blessings
Cat.