Receiver power ratings are a tricky business that baffles even the most knowledgeable enthusiast. Many electronics companies spin their power ratings until they are unrecognizable from the truth and the public rarely has a clue. In testing many popular receivers from the likes of Onkyo, Pioneer, Kenwood, Denon and other 
major brands, it becomes clear… 100 watts is very rarely 100 watts except in the fairytale land of electronics marketing.
To fully understand how watts work in a home theater we need to delve into some engineering, scientific, brainiac stuff. Since I am not an engineer, a scientist or a brainiac, I will do my best here and keep it simple.
One important thing to understand is that watts are important, to a point. The differences between a 50-watt system and a 100-watt system is small, 3 decibels to be precise. Every 3 decibel increase in volume requires that the power output from the receiver doubles. In other words, every time you bump the volume up one notch, say from 30 to 29, the receiver doubles its output watts.
If a watt is a watt, why do equally rated receivers sound so different, why spend $1,000 when you can get the same watts from a $200 receiver. To illustrate how the power ratings game is played I am going to pretend we are selling cyclists, high end brand A is selling the Lance Armstrong model and low end brand B is selling me.
Both brands use a meter on the back wheel of the bike to compile peak output. Brand A does their test while Lance is climbing the steepest mountain in France and find his back wheel is putting out 100 watts and he is moving at 7 MPH. Brand B puts me at the top of a very steep mountain that has no curves and finds that despite my appearance I am capable of hitting 70 MPH and put out 130 watts. Of course if you put Lance and myself anywhere on earth and have us race, I will lose sight of Lance in less than a minute, followed shortly by a heart attack and quite possibly my death.
If Lance was a receiver, Brand A would put his rating down in a very accurate and meaningful way like this: "100W/ ch. @ 8 ohms, with no more than 0.1% THD, from 20-20,000 Hz, all channels driven." This tells us that the receiver was tested over the full frequency range, just like we use it, all speakers driven and using the full frequency recorded.
Company B however gives us a specification like this: "130W/ch @ 8 ohms, at 1 kHz, one channel driven." Unless you enjoy listening to test tones through one speaker at 1kHz, this is not a meaningful specification and doesn’t give us any idea of what the system is capable of.
There is no standard for stating power ratings, which allows electronics manufacturers to legally lie to us. Knowing this fact helps and the sad fact is many of us can’t afford a super high end system so your own judgment has to come into play, you have to listen to the receiver, in your home, on your speakers and decide if it works for you.
Many moons ago the marketing teams discovered that 100 watts was the trigger for the general public and they found a way to get that rating without building a better receiver. The fact is however that unless you have an enormous room or very power hungry speakers, these receivers are more than enough for you. There is a very good reason to consider higher watt amps however.
Higher power gives an amp more headroom, which equates to better detail, truer bass and more pleasant sound even at low volumes. Home theater enthusiast often find they have to turn their receiver up, beyond reference volume to get the detail they seek. This is a sign of a straining system. Doing this also makes the bass muddy and the highs shrill, it is the sound of a struggling amplifier.
One affordable electronics manufacture consistently under rates the power of their receivers and they lose business because of it. Harman Kardon makes high power amps with flagship models showing ratings of 75 and 80 watts, these receivers however easily outperform many models that state 120, 130 or even 150 watts.
The moral of this story is that every purchasing decision requires research, by doing your homework your hard-earned money will buy more receiver. Most stores have a 30 day return policy so you can listen to the receiver in your environment, where it counts, take advantage of this and make a decision based on your ears, just make sure they are located in your favorite chair at the time.