Bigfastmike,
Did you ever have any luck with your Monsoon center project? Just curious. I'm like you, we both want centers for our Monsoon's. I have modified FPF-1000's for fronts, and stock FPF-600 for surrounds. I have Monsoon PC planar drivers too, along with several different small woofers, and "plan" on building a matching center. I may pull and copy the crossover from my FPF-600's, and use that for the center. I also have a couple of old crossovers, from an Infinity Kappa 7.1 speaker. The crossover points should match the Monsoon drivers pretty well. Haven't decided if I want open or sealed planar mids. It may make for better dialog to seal the mids, and tweeter. Less smearing in the vocals, since there will be no rear wall reflection to worry about.
Good luck,
Stimpy