To inject some sanity into the concept,
You can go to a Dolby Digital theater which uses 64 channels and 8 channels for bass. The more speakers you have running at full power, the louder it gets so how loud would 64 channels be at full chat? Deafening! The reason you have so many channels is to move the sound feild around, not to blow up the room with deafening SPL. Never mind 64 channels pulling maximum power alll at once would probably blow breakers or burn the wiring. The concept to drive all the channels in stereo is not a good idea either, it makes and absolute mess of the sound but it is a "feature".
You need to think of it as it is--multiple channels feeding off a common power supply. If the main LCR is going full blast, can you hear the subtile surround effects? No, that won't happen because the blast from the front will dominate and the sounds coming from the back will be blown out and way off axis. To actually hear surrounds, back off the power/SPL going to the front and shift the sound backwards, it being off axis makes it tough to hear with clarity so you reallly need to back it off. The power demands depend on where the SPL demands are located in the sound field, if you "need" high power say to the left, panning to the center then the right---shifting to the surrounds, the amp channels shift that around.
This is multi-channel, not stereo! I keep seeing some weird demand that all the amp channels need to be full power but that is not how it works (unless you like all channel stereo) Say you have a 7.1.6 system and now you "need" full power to 15 speakers--really? Think about how LOUD that would be! Flipping back to movie theaters, do you think the movie companies ever mix a movie to go full blast on all channels at once? That would blow breakers and shut the movie down quickly--not exactly the hot setup for ticket sales. For this reason, movie soundtracks are mixed by professionals and the entire content is scanned to make sure it does not damage theater equipment. The days of a bunch of yokels snorting coke and spinning knobs around by ear are over. 2-channel pan pot stereo is not that critical, once you go to dozens of channels in calibrated theaters for public consumption, the demands to do it right are critical.
The FCC came out with their tests 50 years ago to protect the consumer from audio fraud. They still use the same 2 channel loading test that was modified a bit around 20 years ago. I'd like to see it updated for multi-channel, say a 3 channel load test or something but audio is not important anymore in the greater scheme of things. I'm sure the industry could get together and come out with a test methodology to help the consumer and proivede education to get things clear. Bwahahah! This is audio, it is a tradition to keep the consumer a mushroom.... the last bastion of magic in a technical world.
Yes, my AVR does not do 100 watts on each channel alll at once. It will do 100 watts to each channel when required for a few channels that track the sound field. The mythical (and wrong) way people jibber jabber about "all channels at once" my AVR should be clipping hard, getting hot and shutting down when I turn it to reference levels. It has never clipped, got hot or shut down--not once. To be fair, I don't run it all channels stereo at reference--never tried it but I do know it sounds terrible. What? Another useless feature from audio companies?
Next thing you know some geek will tell me to not use "double bass" because it utterly destroys bass accuracy also!
(don't use double bass)
That being said, it is good to simply things to better understand them--but over simplification causes much more confusion and makes things worse. There is stereo, their is stereo with subwoofers, there is multi-channel and there is multi-channel with overheads (Atmos, Auro etc.) All of those do something different and have different power demands and are setup differently. You are not helping when people ask about how much power they need and give a generic answer--not enough information is provided to even get close.
One last word--it is NOT "Bi-amping" it is PASSIVE bi-amping which means a drastically different thing. Go to a place that sells professional sound equiipment, it can be basic to 6 figures per piece--ask them to show you pro sound gear that can be "passively bi-amped", there is NONE! There is plenty of pro sound gear that can be actively bi/tri/quad amped so you have dozens to hundres of choices. Odd, not a single pro sound speaker can be passively bi-amped but most fiarly expensive pro sound speakers offer ACTIVE bi-amping. Now look back at consumer speakers, how many of them offer ACTIVE bi-amping? I'm sure there might be a few but for the most part I've never seen one (although I don't look too hard) It takes actual skill, knowledge and understaqnding to actively bi-amp a speaker without damage--you do it worong you blow it up. That is fine, if you are a professional you know this and accept the risk going in. On the consumer side, if a consumer speaker had active bi-amping functions--people would just wire it up, fire it up and blow it up. Then trash the speaker on Amazon, cry about it on Facebook and blame the company for making garbage. How many posts on AVS have to do with not reading the book? I don't blame consumer audio companies from not allowing ACTIVE bi-amping--the AVR people could easily add an adjustable electronic crossover setting to AVRs to alllow for proper active bi-amping--very easy! How many AVRs have an adustable electronic crossover for say 500 to 8 KHz to properly bi-amp speakers actively? Not a single one on the planet--not one! No problem, you can give them the "bi-amp" buzzword without dmaging the speaker because the passive crossover is not bypassed--and the speaker companies can blow a buck or two for additional terminals as a "feature". Does it do anything? No, but you "Have" to put that crap on the back of speakers now because that signifies "aduiophile" or something. The good thing is that is chaning, Revel rolls out their new $4,000 monitors with only one set of input terminals, no "bi-wiring" or "passive bi-amping" allowed. This is called knowing your customer, a professional that sees the ability to "passively bi-amp" a studio monitor will think it is aimed at idiots with performance to match. Not a good idea to offend your customer so Revel puts two terminals on the back, not four.
My Friday rant!
Sorry, it just bothers me that "rules of thumb" or jibber-jabber that is wrong becomes gospel while understanding what is going on takes the back seat. Red cars get more speeding tickets so that makes red cars faster! Uuuuhhhhh....