OK, now seriously, what the heck would I do with 180 wpc all channels driven when most of the time my power draw is less than 2 watts to make my ears hurt? Well, if my name was Ian I could throw a party on my dock and play music for everyone on the lake, but its not and I can't.
I used to know all those numbers, but really, it doesn't matter. As long as I have a reasonable amount of power and I don't buy the cheapest receiver on the block I'm getting all the power I need for my system to sing.
You are partially correct you can listen to a Speaker at a moderate volume with only 1 Watt of power, however you need far more power for Theater like volume levels that we hope to achieve ourselves.
SPL Anechoic 1w/1m(db): 87 dB
This means that with merely 1 Watt of power this speaker is able to achieve 87dB which is pretty decent. However most people like to listen a little louder. Like movie theaters who typically have a maximum SPL around 105dB. But I personally prefer a maximum SPL around 112dB which as you know every 6dB is a perceived Doubling in Sound to the human ear.
You have to double the input power to produce a 3 dB increase in sound output
(assuming the speaker is not reaching its limits).
Now to get more than 87dB from the M60 for example you will need an EXPONENTIAL amount of Power Output that FAR EXCEEDS a mere 1-Watt of power. Which is why a big Power Amp then becomes necessary to supply a huge amount of power as cleanly as possible without any distortion which may damage your speaker.
To get all the way up to what most Theaters are capable of at 105dB we would need about 128 Watts, and with my preferred listening volume of 112dB I would need an Amp that can output 512 Watts (See Link Below which uses a speaker with 85dB SPL). So as you can see you need an Amp with a lot of headroom to get your speakers to Full Potential. Keep in mind that All loudspeakers have a maximum power handling capability so keep this in mind when shopping for a Power Amp.
The only thing that wasn't discussed in this quick look was how when you add more than one speaker you get an Exponential growth in SPL. But without knowing how many speakers a particular person is using in their Home Theater I stuck to the basics with just one speaker.
"The key here is that in most or our home listening, there are small amounts of distortion caused by a lack of dynamic headroom. It's the distortion that makes it sound "loud" in a domestic setting. To remove those distortions and increase dynamic headroom relates to even more power. We've become accustomed to accepting some distortion with our reproduced music, because all amplifier's distortion ratings gradually increase as they approach their output limits or slightly clip the audio signals. When that happens, we turn down the volume, because distortion starts to intrude on our listening pleasure, and it sounds "too loud."
The lesson in all this is that you can never have too much power, and that big amplifiers rarely damage speakers. Little amplifiers driven into clipping burn out speakers. In the scheme of high fidelity, that last barrier to realism is having enough power and being able to approximate real-life loudness levels."