Great detailed explanation AJ.
For others curious about how much kmeta to add to their mash or wort, if you punch in the the values AJ gives into the first calculator I linked to you'll get the same answer. It just saves a bit of time and keeps the non chem majors from having to solve equations
AJ: As an aside, when you say, "These tiny amounts are sufficient for biological stabilization of wine (and presumably beer)" I'm not sure I agree. The tiny amounts of molecular so2 *can* be sufficient in wine with proper upkeep, but is highly dependent on pH and oxygen uptake. The pH of most beers is higher than most wines (though there are more and more exceptions - especially in CA!). Molecular so2 is 6% of free so2 at a pH of 3, and .6% at a pH of 4, the normal range for wines. At beer pH it is even less (between .6% and .06% - vanishingly small amounts!). All this assumes you are interested in the anti-microbial properties of so2 for flavor stability (as the OP mentioned) and not just binding up aldehydes.