"Program power" or "music power" is generally given as a spec where music is suppose to be playing at. It's the general idea of where the volume should be and typically half the peak but it's sort of a nebulous spec. If the speakers have a limiting function then there might be something to that.
The fan is a variable speed fan that kicks in when the amp get's hot so you're not going to hear it turn on right away. This might be a possibility that the fan is malfunctioning and the amp is overheating.
To narrow down all possibilities try using it with a different set of speakers, or just one. Do a controlled experiment. Start at low volumes then work your way up. If the hypothesis you are working with is that loud volume is causing the shutdown. Try to find at what point this happens at. Once the amp shuts down see if you can replicate it again. See if it's consistent.
If it all points back to the PMP3000 then I suggest having our CARE department take a look at it.
Your answer kind of made sense Brian, but I'd read a bit about Program Peak ratings on speakers and I didn't realise that it meant my speakers might have a limiting/cut-out capability.
However, trumping all of this is the fact that I also use the same speakers with a different amp when I'm playing very loud heavy metal covers with my other band, and they've never cut out, so I feel sure that it's the mixer/amp.
I'm going to load it up with a few inputs and see what it does; particularly, I'll be taking note of what the fan is or isn't doing. Then I'll get in touch with the CARE Department with my findings