Thanks for the suggestions, guys, but I think that I've got it figured out. I tested the phase plugs with a couple of regular magnets, and they worked just like you would expect steel washers to react to a magnet. So I took some time positioning the plugs on the alnico magnets - a LOT of time. They have to be EXACTLY centered on the magnet, or the magnet wants to repel the washers. Not exactly sure what kind of magnetic field the alnico is throwing out, but positioning is pretty touchy. I wish I had an extra alnico magnet around, just to experiment with. But for now, I've got that great, open sound back that I was used to. So I guess the experiment is kind of a success?