What I find is when the clipping light comes on it's saying time to dial it down a bit. If you need more volume usually that means you don't have enough sound for the kind of event you're doing.When the ETX18sp light comes on it is actually in a state of pre clipping. Still has a little more to go before clipping.
I understand sometimes it's all you have. That's where experience comes in. If you feel you won't have enough sound to cover the type of event someone is asking you to do then you have 3 choices. Buy more sound to do the event, rent more sound or simply tell the client you're not the right DJ for the event.