Magnepan "3 series" differences?

Go to the planar asylum, someone just gave an excellent answer to this question. (Perhaps you're the one who asked it?)

Perhaps you could ask that question there? There are bound to be people who have heard all or most of them. Or look at old reviews, they'll typically point out the sonic changes from previous models -- the one I remember is that they moved the mylar to the front to make the speakers more "alive" sounding. Also, in general, quasi ribbon drivers are more transparent than wire ones, and a better match for the true ribbon tweeter. I think you'll find in general that the main weakness of the old wire Magnepans is the midrange.