While "Watts of electricity" and "Watts of sound" do refer to the same quantity of energy, amplifiers are nowhere near 100% efficient. If they are class D amps, figure on about 40% efficiency. If they're class AB, its more like 25%, and if they're class A you're looking at about 5-10% efficiency. This is of course a generalization, so your mileage may vary.
Another thing that may be worth investigating is the sensitivity of your speakers (the amount of SPL you get from one meter with one watt of energy). If they are high sensitivity speakers, you may find your average power usage to be much lower than the peak power the amp can put out.
A forum community dedicated to home theater owners and enthusiasts. Come join the discussion about home audio/video, TVs, projectors, screens, receivers, speakers, projects, DIY’s, product reviews, accessories, classifieds, and more!