Since most speakers are four ohm whatever the manufacturer says, 250 watts into four ohms from three channels is very good. The rail voltage is 75 volts so that is the sort of number you would expect. That is a lot better performance than a receiver. For domestic conditions that should be plenty. My Quad 909s are 140 watts into 8 ohm and 250 watts into four ohm. That is an awful lot of power to put into a speaker. If you increase power output then you get into very high rail voltages, and therefore dangerously high speaker wire voltages and really require insulated connections, like Speakon, at the Amp and speakers, otherwise their is great danger of electric shock.
In this area you have to be careful what you wish for, or it could be a half day out with the undertaker.