It is not as naive question as you think. Naivety is what the Morons with a so-called full-range drivers demonstrate, feeling that a single driver acoustic system has some kind or theoretical or practical advantage.  Sure, to reproduce “a girl with a banjo” or “a blind grandpa with balalaika” one does not need a lot from playback. However, if one has an interest to get out playback more result with more complex martial then how many channels does a playback need to cover the full range?

Sure it would greatly depending from the topology of channels but my general attitude on this subject is following: the more independents channels properly used is better. The intermodulations, intermodulations and one more time intermodulations. Killing the intermediations is very much a key and to killing the opportunities for intermediations by properly slicing the acoustic channels and properly slicing amplification is in my view is recipe for more fruitful complex sound.

So, what would be an ultimate amount a channels that a truly full-range playback need? Well, probably it would be an infinitely high that would not be theoretically or practically sane or useful. Still, fishing in the mad water of imagination I would propose that 10 channels sounds to me like a very good solution.

•  We do need a LF resonator. The sub 30Hz frequencies live in own would with own rule of engagement
•  Midbass-Upperbass –the most important channels. It might be one channel or two channels – all depends from topology
•  Lower MF channel. I do insist the it is VERY important channel that takes load (Doppler, intermodulation, etc)  out of MF
•  MF channels. It might be one, two or three channels in there performing different tonal, anti- intermodulation, and other duties.
•  HF channel or channels.  Although I would be very conservative in multiplying the HF transducers but I might understand multiple tweeters, one let say up to 16K and another from 16K and up.

So, counting the channels we can see 10 independently driven and independently radiating channels. I think those configurations have a lot advantage to handle complex intermodulated sound.  Most of the loudspeakers out there are losing very aggressively if they care complex sound.  Almond those few that can more or less maintain integrity under complex signal most of them are taken apart by complex signal playing loud.  If you filter out in those cases the problem with amplification, power deficiency, A/B crossover distortion, A2 class, suspension distortion, flux compression, intermodulation in electronics and the rest nastiness and see how different acoustic systems behave then it would be very clearly that the more channels playback has the more volume/complexity stress it can handle. 

There is only one think better then multiple channels - the properly implemented multiple channels. But the “properly implemented multiple channels” are rare and they share the same characteristic as virgins in Paris – both of them are very expensive….