I think the ultimate system would only have two drivers. A woofer and a tweeter. I beleive multiple drivers create to much phase distortion with is timeing errors because of the varying distances of the individual drivers from your ears.
For the same reason the ultimate speaker would have the tweeter in the center of the woofer. Of course with current technology this creates its own problems.
For the same reason the ultimate speaker would have the tweeter in the center of the woofer. Of course with current technology this creates its own problems.