IMO, power guard lights coming on means you are trying to exceed the amp's limits.
It seems pointless to leave the system at a volume where the power guard lights are flashing regularly/frequently. The amp is automatically reducing the gain to keep from clipping, so that should be an indication to turn it down, not just let it ride, so to speak.
As to damage, the amps probably won't be, but hard to say about speakers. They evidently won't be damaged by clipping with power guard, but high power for a long time can also damage speakers if they can't handle it.
EDIT: Oops...forgot to read page two. Looks like most of what I said has already been covered.