Steve,
I'm pretty sure epsom salts are Mg sulphate (or sulfate, can never remember which), not Mg chloride.
reeferaddict,
With the amount of epsom salts needed to maintain Mg over long periods of time, sulphate (or sulfate) in the tank will go out of whack much more quickly than chloride would if using Ca chloride.
I certainly agree with both of you that dripping kalk to help maintain alk and Ca, then use a Ca additive to top up levels when it is required. Mg, on the other hand, is not a component in kalk to any significant degree, and would have to be added in much larger doses than Ca ever would.
Using a Ca reactor with the right media would probably solve a lot of chemistry problems, but I'm never going to have one, and many others are likely in the same boat as I'm in. As a result, I drip kalk nightly and adjust alk, Ca and Mg every week or two, though I should be more consistent and do it weeklly.
FWIW, here's the DIY additives article....
http://reefkeeping.com/issues/2006-02/rhf/index.php