I recall 3 systems where i found reference-level characteristics to which i refer when i consider my own system.
1. 1993 - Apogee Stages, ML pre/amp. The naturalness of delivery was quite startling after all these years. something about the way the voices came thru...no sense of sound being pushed thru a speaker; tonality seemed superb to me
2. 2006 - X1/Grand Slamms and ARC Ref electronics - Scale and effortless like i had NEVER heard before...it opened my eyes to why my personal way of great bookshelves and sub were not the same from this perspective. my CElestion SL6si and Velodyne or Guarneri and Velodyne competed with loads of floorstanders, but not these. They seemed to take any level of signal and delivery all of it in similar fashion to the Apogees but with a vastly greater sense of scale and effortlessness
3. 2011 - Tidal Sunray T1/Tower Sub, all Tidal Ref electronics (3 sets of monos), Argento SMREE, Tripoint Spartan/Troy, STahl-Tek Vekian digital; not the tonality that i felt was correct. Generally too bright. i would take system 2 above this one all day long...and effectively have for those who know my system. But such incredibly vast levels of information being passed thru without any strain, that i was amazed and remain amazed by the number of musical themes i could pick up in the same track i had been using for some time.
I have used it as a reference on that track going forward...and only now have finally managed to approach it at home, having just picked up a second hand Zanden transport to go with my Zanden DAC (finally...after 5 years!...managed to pick up 2nd hand latest specification set and trade in my older Zanden DAC...long patient search but well worth it.)
The only other system that comes to mind is D'Agostino monos, Metronome Kalista Ref/C2A, Ref 5SE, TA Opus cables and the XLF...i know what that system is capable of, and it was not at its best during the demo. That is clear to me...but its noise floor (or lack therefore!) was plainly evident and a new reference for me.