Nice write up! I enjoyed reading your impressions
Your experience parallels many of the auditioning sessions that I have done. Expectations are not always met. Differences are certainly heard, but not necessarily a "better vs. worse" difference. Some speakers really grab your attention while others almost disappear and leave nothing but the music behind.
I'm hopeful that our PM discussions might have helped you a little in at least keeping an ear out for certain specific aspects of the sound rather than just the broad, "I like this" or "I don't like this" sort of judgement. It is often disconcerting to people that they will like a certain speaker in the showroom, only to get that speaker home and not like the way it sounds. That is, of course, the effect of the room acoustics and the seating position. But what DOES translate from showroom to home are specific things like emphasis in the high frequencies, or emphasis in the low frequencies or greater dynamics. Those sorts of things generally remain audible regardless of the room - but the room will interact with the speakers to either make those traits a plus or a minus for that particular environment.
So the trick is to listen to the same speaker in many rooms and to listen to many speakers in the same room. Over time, you build up a sort of knowledge base where you can start to reliably predict how a certain specific trait of the speakers will react with certain types of rooms.
Emphasis in the high frequencies is a common design choice among "high end" speakers these days. Tipped-up high frequencies instantly make a speaker sound more "detailed". You have to be careful though because our ears are very sensitive to any distortion in higher frequencies. We have trouble telling the actual recording from the distortion, but any distortion can make high frequencies sound shrill and fatiguing. Tipping up the treble isn't necessarily bad. If the tweeter keeps very low distortion, you can play it loudly without it sounding shrill or fatiguing. Distortion is the enemy, not just pure loudness. High frequencies are rather easily absorbed, deflected and dissipated. In a large room, you actually need some extra treble energy coming out of the speaker, just to make it sound like flat frequency response at the seat. This is the case in movie theaters where the room is very large, the walls are acoustically treated and there are many bodies in the theater. All of those factors serve to absorb much of the high frequencies, so movie theater speakers are actually "bright" - as are the mixes themselves. Measure them with a mic placed very close and they would show a rise in frequency response in the treble. But at the actual seat, the frequency response is much flatter.
All of this is to explain what might be going on with those Vandersteen speakers. I haven't heard them myself, so I cannot say for sure, but it is certainly not uncommon for speaker makers to purposely emphasize the high frequencies. If they are doing it without distortion, the speaker will simply sound more detailed, clear and "snappy". But you have to be VERY careful with such a design choice because ANY distortion will also be louder and thus, the speaker can become fatiguing much more easily.
Your experience with the PSB speakers certainly mirrors my own. I have always found PSB speakers to sound rather "veiled" and somewhat "flat". PSB's design is the exact opposite, with rolled-off high frequencies as a purposeful design choice. In smaller, reflective rooms - much of the high frequency energy is bounced off of the walls and is NOT absorbed. The net result is that even a flat speaker might end up sounding "bright" in such a room. By rolling off the treble, high frequency distortion is almost completely avoided. People often flock to this sound because it almost never sounds shrill or harsh, but it comes at the expense of some detail IMO. I've actually found that a lot of people who started with Bose speakers really love PSB. This is not surprising to me. Bose speakers lack ANY output above about 8 kHz and everything up to that is a distortion-laden mess! People who have been listening to Bose hear the PSB speakers and it is a revelation! The distortion is gone - that is a HUGE improvement. And they never notice the lack of detail because the PSB speakers go well beyond the 8 kHz range, so, to them, the PSB speakers sound PLENTY detailed
So the Paradigm comparison - very interesting.
For one thing, Paradigm really does have a clear design goal with their speakers and they use it pretty much across their entire lineup. They aim for a scientifically calculated frequency response based upon the research that is conducted at the NRC. So it is not at all surprising when the Mini Monitor and the Studio 10 and Studio 20 all sound far more alike than they do different!
With the Monitor Line though, you've got a pretty big difference in terms of efficiency. The Monitor Line really was designed with the idea that they would be driven by mid and lower level receivers, whereas the Studio Line has the expectation of more amplifier power. Much of what you heard can be attributed to the difference in efficiency. More efficient speakers also tend to be more dynamic. It takes less power to get their drivers to move or to move farther, so if you turn up the volume knob the same amount with the Monitor Line vs. the Studio Line, you will not get the same increase in loudness. You have to turn the volume knob up more with the Studio Line, so that can be the source of audible difference much of the time.
There is little question though that the Studio Line uses more sophisticated drivers that produce lower distortion. It is often counter-intuitive because a very low distortion speaker that is also very linear and very flat in frequency response will often sound less "exciting" or "distinct". This is certainly the case with subwoofers where most people are used to hearing a TREMENDOUS amount of distortion and when it is gone, the undistorted sound seems too "quiet".
This might sound ridiculous at first, but I've found a very handy recording that I now use to instantly identify speakers that have any distortion or "overhang" in their midrange. Some people will laugh at me for this, but it is Kris Allen's version of "Heartless" from American Idol - lol
At the very beginning of the song, Kris is singing with very little musical accompaniment. If the speaker is distorting or lacks nearly perfect transient response, it sounds as though Kris' voice has been recorded on multiple tracks, with the end of one phrase seemingly over-lapped by the beginning of the next phrase in the song.
With speakers that have extremely little distortion and virtually perfect transient response in the mid-range though, you can plainly hear and separate the reverb (which causes the end of Kris' phrase to linger) from the breath and beginning of the next phrase. The effect is that it no longer sounds like multiple tracks that have been poorly over-laid, but a single track that simply has reverb on Kris' voice. If the speaker is distorting in the mid-range, that reverb "melds" with the breath and isn't easily picked out as reverb and if the speaker lacks nearly perfect transient response, the reverb sounds as though Kris really continued singing, which would make the beginning of his next phrase impossible and thus, create the effect that there are multiple tracks over-laid on top of one another.
If you're willing to face the embarrassment of downloading an American Idol song, I can easily recommend having this track, purely for this test
You only have to listen to about 10 seconds and it can quickly tell you so much about the capabilities of the speaker!
I should note that it's entirely possible (and likely) that the song WAS recorded on multiple tracks. But you can be sure that when they were mixing it in the studio, they intended for it to sound the way it sounds on "good" speakers - where you can plainly make out the reverb from his actual voice and believe that he was simply singing straight through, rather than the way it sounds on "bad" speakers - where it plainly sounds as though there were multiple tracks used.
I haven't tried this out on the Paradigm speakers, so if you're planning to go back and listen to them again, I'd love to get your experience of how that particular song sounds on the Mini Monitors vs. the Studio Line