Richard, you should understand that you might never reach max power output; merely turning the volume all the way up doesn't do it. At typical comfortably loud listening levels(such as your -20)the speakers are using about 1 or 2 watts. Extreme peaks in the music might draw 50 or 100 watts(at the same -20 setting)for a few thousandths of a second.

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Enjoy the music, not the equipment.