Jack, you should try to read the data sheet yourself. Even if you don't understand it, read it a few times and most of it will start to make sense. Then when you come for help on the forum you will be better informed and we will be able to help you more easily.
That being said AG pointed out a good chart from the data sheet. It shows the power output of the amp (on the left) as the voltage increases (on the bottom), just remember that the voltage listed is for a dual power supply, so a 15V supply on the chart would be a +15 -15 supply.
I also think that you may have been mistaken, the IC enters Mute or Stand-by mode when the input is between 1.5V and 3.5V. You can add a voltage divider to make the voltage withing this range. If you do not want the IC to enter Mute or Stand-by mode, connect these pins right to the positive power supply.