Tom, as the previous replies indicate, you set the volume levels for the various speakers equal to each other during calibration by using a test tone which sends an equal voltage to each speaker. During actual use with program material however, there's almost never a situation in which all the speakers have to play at the same loudness level, especially the max level(this is why the "all channels driven" power rating used by some manufacturers is less realistic than the standard 2-channels driven rating). The watts needed by a speaker during actual play might vary between the maximum and zero. The surround channels are often lower in level than the main channels.
