P.A.? That`s a job for the BASS player
Our bass player's got a PA, but only in his day job and she goes home each evening. If it wasn't for that he wouldn't know how to spell PA, let alone rig one.
You need to know each amp's power rating compared to the speaker its driving. If you are exceeding the "amp rating is up to twice the power of the speaker rating" rule, e.g. you are using an 800W amp to power a 200W speaker, then a slight reduction on the amp's volume control might be in order as a safeguard. In this instance a 3dB cut is all that's required. As Ivan said and as you will find on this forum time and time again, it is vital that you do not drive the power amp into clipping, so do not push the amps too hard from the mixing desk. Most power amps will be producing their maximum power with a +4dBu signal, so if you've got their volume controls turned right up and you are sending more than +4dBu, then the amps will start to clip.