I know that there has been quite a bit of speculation as to what Magnepan changed with their recent introduction of the revised Magneplanar 3.7i. The company has been quite secretive about exactly what the modification consists of, just claiming that it makes an audible improvement. I recently came across this
press release regarding the 3.7i from the UK which I thought could clear up some of the confusion. You can see in the fourth paragraph that they mention a newly re-engineered time and phase aligned crossover. This type of change would be consistent with the requirement to ship the speakers back to the factory to have the upgrade installed and the cost of $500. Hope that you find this information helpful.