Hey John,
The master volume is a combined sum of the RH and acc on the PA800 ... the only perceived difference in sound from a volume change on a digital instrument is how it reacts in the room. There is no sonic difference if it's low or high output, unless it's distorting the speakers. I used my powered rigs many, many times at small venues and had great results. Sometimes, if you're "almost" there, but need a little "ooomph" .. just add a small bass amp, or the Bose compact without the extender poles for some enhanced low end. It'll keep the room volume down and add some punch.