Steve,
Think of a calcium reactor that instead of had calcium based media, but sulfur based media. Get a slow enough flow through the media, the anoxic zone will host the bacteria responsible for reducing nitrates, and viola, a denitrator for your system.
Here's a blurb Delbeek wrote up on sulfur based denitrators a while ago for AFM:
http://www.aquariumfish.com/aquarium...id=3802&search
There are also several threads on them over at RC of course, if you wanted to poke around over there.
Greg, I'm not familiar enough with Zeovit to comment whether it's a similar process or not. My gut instinct tells me it's different though, because I thought Zeovit was supposed to be a fairly expensive (as in, ongoing expenses) methodology, including dosing several things, whereas a sulfur denitrator is in the same "set and forget" category as a calcium reactor -- i.e., a perhaps hefty one-time/initial cost, but the ongoing costs are minimal. But again, I'm basing this on ignorance of the Zeovit philosophy so maybe someone who knows the details can comment on whether it's similar or not.