Maybe the power amps aren't the best match for the maggies demanding load.
A lot of folks like to run them with high power solid state amps, and yet they were originally partnered with AR tube amps.
Are you running the correct transformer taps on the amps for the speakers?
And of course it could just be that you are not getting all the power you are paying for from the electrical company, especially in the summer months.
If you can, check the voltage from your receptacle (if you don't know how, hire an electrician) and then if it is below acceptable rating, call the electrical provider and ask them to check things out and up the voltage to your house.
Years ago I had a pair of Metner mono blocks that kept shutting down.
Ed fixed then twice, and had me do a check on the voltage and sure enough it was low.