I'm looking at adding a sub to a full range PA setup. Our powered board has a sub-out, so I need to know if there are sub signal processors? Are they even necessary? I've also seen plate sub amps. Does anyone make pro grade plates? These plates appear to have some mixing, phase control, x-over freq, etc. Just no pro connectors, or other features.And some of these plates can't run at full duty cycle ( some stated 30% duty cycle !). Any thoughts?