drashp,
Excellent points you've made. I will expand on that by saying that frequently power ratings for A/V Amps are given for one channel driven. Now, if you drove all channels, you would quickly run out of BOTH Voltage and current.
As an example, I bough a small power supply transformer from Radio Shack, let's say for this illustration, it was rated as 24volts and 5 amp. What I discovered was that you could have 24 volt OR 5 amp, but not both.
As the current demand goes up, the available voltage drops down, and that is true to greater or lesser degree on all power supplies. Now drawing current for 7 channels from a single power source, means less voltage and therefor less current available to each amp.
Now some comments on power in general. When you change the perceived volume of your stereo by 3db, you have doubled the power. To put 3db in perspective, if you nudge your volume control up just enough to notice the change in volume, you have increase it by 3db. Sound wise 3db isn't much, but again, power wise, it represent a doubling of power.
Now, as a point of illustration, lets say you are cruising along at a health 50 watts. Now you nudge up the volume just one small notch, BOOM, now you are cruising at 100 watts. One more tiny nudge upward of the volume control, and BOOM, you are cruising at 200 watts. Yet, the overall perceived volume has changed very little. It will be noticeably louder, but not substantially so. And there are your blow speaker. That one last nudge upward pushed it over the limit, and snap, crackle, pop, buzzzzzzzzzzzzz ...blown speakers.
Do you see how see how easy that makes it to blow speakers? Just one tiny notch above the reasonable limit and you have overpowered both your amp and your speakers. That's why I say, it is always the guy running the volume control that damages equipment and not overpowered or underpowered amps. Again, rarely, and only in the most extreme cases have I ever gone over 60% to 65% turn of the volume control. That will fill any average room to painfully loud levels.
On the other hand, outdoors or in a large hall, that same 60% is going to seem a little weak. If you are going to play a large venue like that, you need lots of speakers to push lots of air and tons of first rate high powered equipment behind it.
Steve/bluewizard