Blindjim,
First, my perspective, so you'll know how flawed my interpretation is...and subjective.
I have heard everything from Wilson's best at $130K, to MBL's best, at I think, $119K, to the other mega priced speakers. When I heard these, on one occassion, I was at a dealer, (Wilson's), but heard them (his current best at the times) on numerous occassions, at the CES too. The MBL's only at the CES.
First, just comparing these megas,(I am sure others will pick from thousands of other megas) these two are very different speakers from one another, certainly design wise, as well as performance wise. To my ears, the each do different things well. The Wilsons are more dynamic, and have an obvious bass extention edge, both in terms of slam and frequency response. Yet, to my ears on the occassions that I have heard them, the Wilsons just don't seem to disappear completely. I asked my two cohorts and they both made that statement without prompting,(industry types) that they were not as transparent in terms of dissappearing as we might have thoughtthey would be. But you asked how megas differs from $10 to $40K speakers.
So, how are both different from the $10K--$40K speakers, of course leaving out diminishing returns because that should NOT be considered IMHO, because that brings in too many other thoughts, but we can discuss that off the site. They have more resolution at almost all levels of SPL, better micro dynamics, image density, front to back imaging, width of soundstage, (though the cabinet locations were, at least to my ears, again obvious on the Wilsons). Keep in mind that they are mind boggling good, by any standard, just this one issue of, I guess cabinet noise clues (?), and EVERYONE can have different thoughts, and I am sure they will. Maybe my samplings were both limited.
Down to earthly pricing,(ha)Let's compare them first to the THIEL CS5i, which I owned for several years, which cost about $12K in 1989 dollars. The Wilsons as you might expect have more resolution, so the clues as to 'where' things seem to happen in the sound stage become more well defined. Imagine a photo that is crystal clear, versus a polaroid. Though not a great example, telling nonetheless, the lesser speakers offer less resolution of the overall sound--same thing, different sense (hearing vs sight). The overall sense of realism is greater with the mega speakers, in terms of "Am I really there?" Real music, acoustic music for sure, to me, as an event, is sort of'unspectacular', its just, well, real music. Noone goes into a hotel lobby and hears a piano coming from the bar and says, "Oh my God, a real piano!" They can tell though, if they're careful listeners that it is a real piano and not a recording, because of the subtle, (think low level res) clues that they pick up on. So, with the Wilsons, those subtle clues are more abundant, therefore they sound more,'real'. This inspires a memory, which is, back during that era, I talked to JT about the 5's and told him that I thought that the CS5's had MUCH greater 'image density' than any of his previous models, and assumed it was because each driver was working more easily thoughout its frequency askance.
In the '90's I came to be very close to the Nearfield Acoustics, which cost up to $90K in those dollars. They too, (regardless of varying opinions) offered incredible dynamics and image density. (The largest had, I think 24, drivers operating from 65hz to 3Khz. Then 48 domes operating to above 35Khz. Then two 'depth charges' for subs, 2x18' subs times two. Whoa, bass extension.
People have faulted them for comb filter effects, (cancellations due to proximity)as well as various other perceived faults, but they did some things VERY well, and offered that incredible density, I mentioned. This is, to my ears absent in virtually all driver based speakers, with limited drivers. MORE IS BETTER?
God, I am going on like an idiot. Well, the differences, to me, is frequency extremes, (mostly bass) dynamic range, image density, soundstage, (width and depth). With these qualities comes greater tonal purity, at least on the better Mega priced speakers.
Like most engineering issues, there's nothing like throwing money into a solution. More, of course if done thoughtfull,should be better and better costs more.
Jim, I should have given you a three word answer, "Sense of realism."
Sorry to prattle....
Larry