I too have Magneplanars and your description is exaclty the effect I am talking about. My question was also prompted by a post on the High Efficiency forum saying that the JBL woofers needed to be played loud "because of their stiff suspension".I am almost ready to take the jump and make a pair of 4 pis, but I wanted to be sure that they wouldn't suffer from the "Magneplanar Effect".
Thanks,
Brian