Because Magnepans have a nearly ruler flat impedance across the audio spectrum they are much kinder to tube amps than their efficiency rating would otherwise indicate. What amp are you currently using?

I've used my MG 3.5s happily with Jadis Defy-7 (100 W) and Antique Sound Labs Hurricanes (200W). Although Maggies are not very efficient, they present a fairly constant and easy load to the amp.