Johnto is spot on. My class D experiment with 290w mono bridged also failed and the Maggies clipped the amps at 82db in dynamic passages.
What I found was that the key is the Power Supply and the Capacitance. My Odyssey has Dual 400 VA transformers, 180,000 AuF Memory and provides >60 amps delivered current. Hence, the Maggies sing without the slightest struggle. Choose Class A/B direct coupled, Loads of memory & current delivery and you will not have to learn the expensive lesson buying again. Do not get lost in looking at Watts but focus on power details and the ability of the amp to store enough power to handle dynamics that push you down into 2ohms.. Bryston & Odyssey will do nicely. Consult with other Magnepan owners as well. Cheers.