Single vs Multiple driver loudspeakers...

What are the pros and cons between Single Driver loudspeakers and multi-driver loudspeakers? The arguments with single driver loudspeakers are that their simplicity makes them easy to drive, plus the x-over-less setup improves dynamics, not to mention no phase problems. The thing I read is that no single driver can possibly produce the full range of sound, and most necessitate a subwoofer. On the other hand, multi-driver loudspeakers can offer a full range, but some say that more than one driver introduces phasing problems to some degree.

I have a multi-driver system that sounds great. How would a single driver setup improve my sound, if at all? And if single drivers are that much of an improvement, why are they harder to find(at least for me)?

I have also read that multi-driver loudspeaker more than often need to be paired with a high wattage amp because of the lower sensitivity, ranging from 89db and less, while single drivers loudspeakers are great for low powered tube amps because of their higher sensitivity.

Most of this, is what I have read, but never really heard.

Can someone educate me?
I have a trio of the Lowthers R L & C. It will be hard to go back to cones.--(Deaf old guy) These embarrass my 9k speakers in the midrange.Oh ya' nothing below 50 hrtz or thereabouts.
I have been enjoying the single driver/SET experience for about 6 months now. I still have my Maggies and Apoggees. I'll keep them all. The single driver has a coherence that I have come to appreciate after 7 yrs with planars. As far as having to add a sub, I would rather "crossover" a woofer at 60Hz or less than what most multiple driver systems do at 200hz or more. Plus, you can place the sub in its best location. As far as the upper Freq's, I haven't felt I'm missing much. I hear the brushes on the cymbals quite clearly. If I feel like I need a little more air up there, I will add a super tweeter which would "crossover" around 12khz or so. For me it would be a system that had no crossover between 50hz and 12khz which is where alot of the music reigns. I have both push-pull tube and SS that I use on the planars but the Fostex seems to sound best on tubes especially SET.
Gmood1, just look at the possibilities of using the Clari-T's. Get a killer Universal Player that can do distance adjustments and hook up several of these with single-driver-high-efficiency speakers!
Matchstikman, sorry for hi-jacking your thread.