Ironregime - in fact, the place I first got those copies from was the local library.
Gneech - yes, I know the place well. I grew up in upstate NY and my dad LOVED to go on retreats to various catholic monasteries. Sometimes he would drag me along. I would bring the latest sci-fi/fantasy novel I was reading (mostly age 10 - 13 at this time) and would hole myself up in my room in the guesthouse and read away, coming out only for meals or to walk in the countryside ... some of those places were in very beautiful spots. I even had a huge flock of sheep and a sheepherder!
ANYWAY, back on topic, I also heard some stunning Gregorian chant in these places.
For the deep throated singing a 'la the dwarves image, though, you really have to go either to the Slavic peoples - Bulgarian, Russian, Serbian, etc. OR to those Tibetan monks. Ever heard them growl away? Eerie but amazing. THAT would freak me out if I heard sixty voices singing like that underground. Of course it's not really a capella so maybe not what you are looking for... Hmm. Well, guess the Slavic people are your best bet still.
Be aware, Slavyanka specializes more in folk singing, and especially humorous folk songs. At least they specialize in them in the sense that they perform them more than any others percentage wise. Perhaps b/c of the audiences???? Dunno - but the Salvic peoples specialize in melancholy, beautiful songs. Stuff that is hard to find.
If you want REALLY deep voiced chanting ... look for the name Igor Ushakov or Ivan Rebroff on amazon.com ... the one I have with the first is called "Orthodox Shrines of the Russian North", and the way he sings in there is so low it should be outlawed. But then there is Rebroff. That's just sick. I have "Christmas with Ivan Rebroff" and he sings the German Christmas Carol "Still, still, still." Absolutely sickening. No human being should sound like that. He sings as high as an operatic alto and has hit the lowest recorded note in human history. He puts the bass from the Fairfield Four to shame! And that's low....