Pass 250.5 shuts down driving Magnepan 3.7

This is my first post so please bear with me.

My Pass labs 250.5 protection circuit shuts the amp down when I drive my new Magnepan 3.7s at high volume. I'm talking about a volme higher than I might consistently listen, but not an unbearable level.

I'm using a Cary Slp 05 preamp with long balanced ICs (25 ft,) The amp is close to the speakers with less than 6 feet of speaker wire. The system works fine at normal volumes. I've tried the same thing with a pair of Cary MB500 (750 W @ 4 ohm) and they too shut down at high volume.

I believe the maggies drop below 4 ohms and I wonder if either amp can handle the impedance drop below 4 ohms.

Has anyone experienced this issue ?

Any suggestions ?