dancerjack saidi don't remember the composer/title, but i heard an a cappella performance by the vienna boys choir that was extraordinarily layered in the harmonies, while the melody and counterpoint interwove in such a way that it somehow sounded like ocean surf on the shore... does that ring any bells??
that might have been Tallis 40 part motet "Spem in Alium" .
By the time all the parts interweave together you get that massive rolling sound indeed.
i prefer the mixture of instrumental and vocal , but for strict a capella,
the Allegri Miserere comes pretty much at the top of my list.
but there 's also some fun stuff by Steve Reich .
and i also really like Elizabeth Poston's "Jesus Christ the Apple Tree".