Hi David,
Speaker endurance and what happens beyond the max power rating are things that are not discussed enough in my view. We have invested a lot over the years in improving our driver designs to withstand enormous amounts of power. We have an endurance test here that all our products have to go through and pass. It is heavy metal music played at 1.5 times the max rated power for 100 hours continuously. We have done this test at double the rated power on the M80s and M100s and they both survive it. Personally I think this sort of testing is important. On the surface it does not seem to have much to do with the quality of the sound but does have a lot to do with the overall quality of the product. And it does affect the quality of the sound as you approach the limits.
An ADA1500 would be perfect for what you are trying to achieve. It would make your system play really loud and clean; and the M80s can take it. Though the M100s would be even better suited for it.
