Looking for info on speaker loads?

I am running the integrated amp: NAD M33 and recently changed speakers. 

From KEF LS50's to Magnepan LRS.

For the first time ever I'm getting a warning that my right amp is over heating. As I go up in volume, a tad higher than normal listening levels but no where near ear splitting levels. 

I emailed NAD and they said the M33 can run the Maggies mw/o issue.

The speakers now and before have REL t/5i tried to them, the music is nothing hard to reproduce i.e. Sam Cooke coming off of Bluesound Vault ripped CD's.

The forum members here have much more experience then I do and was hoping to get some help, insight to solve the problem or at the least understand the problem, of course I've heard often that the Maggies are hard to drive.