paul of hot springs

So I have a pair of heresies and a pair of la scalas. Both of which are rated at 100 watts rms. I currently have a power amp rated at 100 watts rms per channel, with a channel A and channel B speaker switches. My system gets to go outside on occasion. to play so I want a full 100 watt power to both pairs. Do I need a second amp, one for each pair, I'm thinking maybe when I use both the A and B switches only half the power goes out to each pair. I'm using a SAE rack with the A202 amp; would I get more volume using separate amps for each pair