Back in the day, when Wendell was at Audio Research, they marketed together for a few years. We sold a lot of Mag/AR systems as they were great together--still are, by the way.
Trivia for those who do not know:
Audio Research EC-3 electronic crossover was made to work specifically with the Tympani I-C speakers and the EC-21 active and PC3 passive crossovers were made specifically for the Tympani I-D speakers.
SO, speakers as revealing as a Magnepan need the best stuff driving them. Since AR and Magnepan have been "broken up" since about 1975 or so, not surprising that they might want their own amp.
By the way, since I still listen to two pair of Tympani I-C speakers, if anyone has an EC-3 lying about gathering dust...
Cheers,
Richard