DJ, it isn't a matter of "protection" ; it's how to get the best sound out of the combination of sub and main speaker. There's no danger in these smaller speakers being run full-range(as they have to if there isn't a sub)it's just that the sub should be able to handle the frequencies under about 100hz better and should do most of the work there.
It doesn't matter how much power an amp can supply; a speaker will only draw as much power as it needs at that instant. Therefore a speaker doesn't "handle" the full power that an amp is rated at.
