wow, thats low....but every album sold is probably sold to a very strong fan base. i'll bet that on their next album, they will sell at least half of that in the first week.
As far as underground music goes, that's okay, but far less than I expected.
Sepultura's Arise(pretty nonmainstream album if you ask me) sold in excess of 1,000,000 worldwide and charted #155 in the Billboard Top 200 Albums in te US.
Arise has been out for about 13 years now so I don't find it too hard to believe that it's sold that many copies....besides, that album kicks major ass! At least it's not one of their newer albums selling that much.