It's not about the volume but ability to more accurately reproduce the source material. By adding more, differently sized drivers, you can better task each driver to focus more on the frequency spectrum it was designed for. For example, a subwoofer could play a 20khz tone... just not nearly as well as a tweeter!
So, the same should hold true of the difference between the M22 and M60. By adding dual 6.5" woofers, you are freeing up the 5.25" mid to focus more on it's frequency range and ignore the lower end (though proper crossovers). Same goes with the M80 where the dualing of components likely allows for each driver to focus on a more narrow range of frequency to more accurately reproduce the sound.
However, I'd argue that you only really need this if your room is large or you are a hyper critical music listener and appreciate being able to pick out the oboe's from the clarinets. In a home theater environment, so much of the mix goes to the center and subs, the rest of the speakers are there to blend in. This is why many people like little cube speaker systems.
Last edited by TDIPablo; 06/05/18 05:25 PM.