Most educational audition you ever had?

What's your experience? Not what was the best preamp or amp or speaker you heard, but what audition changed your pre-conceived notions of audio in one audition, for better or worse? What was the most educational? Where, when, what, and why.
I've had the pleasure to audition various pieces of audio equipment for the last 25 years or so at dealer showrooms, audio shows, and fellow audiophiles' homes. But for me it was an audition of Revel Studio (the newer version) loudspeakers with all new at the time (500 series ?) Levinson equipment at a dealer's showroom in Northern Virginia, about 2 years ago. I went in only to look at CD/SACD players (from Marantz or Esoteric) but heard this system.
What was educational for me? I found a CD they had that I was familiar with (a Living Stereo or Presence SACD of Gershwin Rhapsody in Blue), and having listened to it in my own system over the years, with changes in homes, rooms, and equipment, what struck me was the soundstage -- something I had never heard before. This soundstage on this older recording, on this system, was confined to a box about 4' by 4' between the speakers, much like a TV. It was like it was cut out with a scapel. The speakers were probably 10' or more apart and I was at least that distance from them. The edges of the 'box' were very distinct - something I have never heard before or since, that is, there was sound from the box and not anywhere outside of it. Almost weird. The dealer did have a good system set up and room, something many of my auditions over the years have not had. So I'm sure that was a big contributor to what I heard. Anyway, for me it was a first, in terms of how distinct a soundstage could be compared to so many other systems and rooms.
So, as to the question of the post, I am not saying it was or wasn't the the 'best' system I ever heard, or the last word in any one category of bass/treble/realism, or musicality, (except soundstanging in my case), but in this way I described, it was very educational for me.
What was yours?
Trelja, Technology that stands the test of time usually stands the test of mine:)
It would be nice if members here displayed their A'gon moniker on their shirt at shows. Everyone with half an ear liked that room, so I could not pick you out:)
Most educational was, without a doubt, the difference an upgraded preamp made in the system. The sound was consistent with what I thought would be the result of a better amplifier - more power, articulate bass, etc. A good preamp is much more than just an input selector and volume control. But like everything else in this stupid hobby, a good preamp costs good money.
+2 Mrtennis.

Isochronism, "At the 2012 Waldorf NYC Audio show the room with the Quad speakers was the best sounding room to me by a good measure."

I absolutely agree with you. In fact, after hearing Robin Wyatt's room, I put my money where my mouth is, and bought a pair. After living with them for more than a year now, my enthusiasm hasn't at all diminished.

Most remarkable that in the age of five to six figure loudspeakers, one introduced almost sixty years ago, and obtainable (depending on condition and/or restoration) for $750 - $5000, can leave that kind of impression on folks.
At the 2012 Waldorf NYC Audio show the room with the Quad speakers was the best sounding room to me by a good measure.
One that comes to mind was an all-Rega system at the last San Francisco Stereophile show. It was a modest system that really made music as well as making a big impression on me. There are a lot of audiophile niceties that we get drawn to but I always have to be conscious of the balancing act between getting off on the sound vs. getting off on the music.
Mrtennis, how right you are .
the first audition of the quad esl. to this day that speaker comes closest to the real thing.
My epiphany came when I finally got to listen to a pair of Legacy loudspeakers I'd lusted over for several years. I'd gone over them in the mailings I routinely received more times than I could count. Everything seemed perfect: lots of woofer cone area, midrange totally accounted for, and a state of the art tweeter section. The quality of the cabinetry and finish was stellar. And, with a practical and seemingly brilliant engineer, surely the crossover had to be as good as things got as well. With all those drivers, the speaker looked the part, measured (if such a characteristic exists) perfectly, and had loads of testimonials showing how customers found the right speaker after the typical audiophile journey. Who could ever need more in a loudspeaker? It just had to sound perfect. Had to!

While the speaker sported a price I'd not blanch at today, at that point in my life, it was kind of a stretch. But one I planned to make. The mail order might happen any time. Wait, a used pair just came in on trade at one of the big local brick and mortar audio stores (remember them? wonderful places to spend time in). Not quite the veneer I would go with, but a price I could easily swing. OK, my lucky day. Done deal! Since I knew the staff, they asked me to come over, and give them a listen before going through with things. Ah, come on, the decision was already made. All right, all right, all right. Just a formality so I thought, these babies were mine. So, there I was, favorite music in hand, ready to roll. Get ready to throw them in the back of my Bronco, I already folded the back seat down two days ago. They had them set up with a great muscle amplifier. I was ready to ride Space Mountain. Here we go, and uh, um, nothin'. OK, let's try a different CD. No, maybe switch in another amplifier. No? Preamp. Still no good? How about the cabling... I had another speaker do this to me before, but these? My dream, my destination product. NO!!! I mean they left me as disappointed as I'd ever felt in audio.

The (single most important in all the hobby) thing it taught me was that drinking by the label in audio puts one in a very dangerous position. Specs don't tell the story, neither do reviews, or the opinions of others. You NEED to listen to a component, and judge it with the one instrument man has not yet come close to bettering.
About 5 years ago, a demo by Roy Gregory at the UK National Audio show. It was of a good mid price system, from memory, Electrocompaniet integrated and CD player into Kef Ref standmounts. This started on a basic shelf, then progressively moved through a top flight shelf, better interconnects, speaker cables, then power cords, then a Nordost QX4 then Stillpoints under the speakers.

I would recommend just such a demo, for any tweak naysayers. It really was very emphatic, with each addition making an audible change, nowone in the packed room denied. The most impressive change was the Nordost QX4. I bought one and it is still there in my system, making a real, worthwhile difference.
The first time I heard electrostatics in the early 80s. Was shopping for speakers when I happened into a room with Acoustat 2+2s playing. I stood in the sweet spot soaking up the new-to-me sound until a salesperson noticed and proceeded to patiently educate me on the strong points and how to listen. Probably influenced every purchase since.
Les Paul and Mary Ford at the Penta Hi-Fi show in London in the 90s. Same song and recording. I think it was a Roksan versus a Krell CD player. The LP absolutely trounced the CD.
It was more than 20 years ago.I bought a VPI turntable and the dealer had just finished tweeking the set up of my arm and cartridge.He was playing Famous Blus Raincoat which he just happened to also have in CD format.He had been trying to get me to convert to digial because as he said back then "vinyl is done."
When I felt the table was correctly set we started the comparison.He put the CD on his Wadia and we listened.After about 30 seconds he stood,shut the Wadia and never mentioned digital to me again.
"03-03-14: Tostadosunidos
Regardless of format (TT vs. CD) I would expect the results to be very recording-dependent. I gather the CD and the LP were not recordings of the exact same material."

It was actually the same recording. They used a Jazz album. Honestly, I don't remember what it was because I'm not too into Jazz. Also, after reading my first post again, it kind of looks like I'm bashing digital. I'm not. Remember, this was 1990-91. CD playback has made some incredible progress since then. I still think vinyl is better, but gap is much closer.
All mbl demo at United Home Audio in MD a few years back using CD, phono and reference RTR recordings, and in a showroom suited to bring out the best.

This system in general was all time home audio imaging and soundstage champ I have heard and all the unique aspects and limitations of each source type were laid to bare.
There was one decades ago for gig I wanted to join when realized I really suck.
RMAF MAGICO Q3 wonderful!!
Regardless of format (TT vs. CD) I would expect the results to be very recording-dependent. I gather the CD and the LP were not recordings of the exact same material.
Winter CES. I'm pretty sure it was 1991, but maybe 1990. Went into the Scientific Fidelity room and was completely blown away by the sound. The system just sounded great. Word got around on how good the sound was and there was a line down the hall. Everyone was talking about it. The next day I went back to hear it one more time. I believe it was the last day of the show. It was just OK the 2nd time around. Didn't sound anything like the day before. After the demo, I went up to the people from SF and asked them what happened. Why did the system sound so much better the day before? They said they were using a TT as a source yesterday and that today's demo was with a CD player in the system.