Based on the Magnepan 3.6R’s that I have, class D sounds fine. I have the NAD M33 which makes about 380WPC into 4 ohms (also will do over 600WPC peak). So yes, the bigger panels need some juice to make them rock. After hours of listening, they still sound great and the amp only ever gets slightly warm, even with the volume set at 0.0 db
As to how they sound, I’d describe both the speakers and amp as neutral and I mean that in a complimentary way.
I compared the M33 with various AB amps that were quite a bit more expensive, one or two that were considered "warm", and I simply didn’t hear the difference. I’m sure some will claim my ears must’ve been blocked that day, but no, months later, I’m still impressed with the sound from this combo both on modern music, classical, jazz, and even country.