I’m gob smacked. What were you’re aha moments?

 There certainly have been several really excellent milestones. Like going from a Khartago to I Kismet Reference from Odyssey. But sometimes it’s a small change, usually inexpensive, that makes an unexpectedly great change in SQ. ...
Herbies decoupling sliders under the spikes of my Aria 936s. Improvement in clarity and presence is stunning. 

First time listening to my roommates Quad 57s in 1973 or thereabouts, in college. He built his own solid state amp which was a state-of the art design in 1972. The thing got extremely hot playing the Rite of Spring, but it kept going. Those 57s were unforgettable, but I did not get my own Quads (2905s) until 8 years ago. They are keepers.

Listening to Vandersteen 2ci powered by Jeff Rowland electronics circa 1989 at advanced audio systems in Tacoma Wa.  Just sold them last year. Song was Bob Dylan's " man with the long black coat".

(great thread) I'll keep it in the last 5 yrs, since all my really big 2-channel moments were 35+ yrs ago.

I have a pretty robust desktop system. For years I got along with less than audiophile 2.1 speakers/sub. Pretty good, but not as good as possible. Last year I bit the bullet and bought a pair of ATC SCM 12 Pro's. DAMN! Not only are they the best 2-ways I ever heard, but they manage an extreme tightrope-walk of great accuracy w/o sounding edgy/tiresome. Great monitors.

The other big moment was finally getting a non-oversampling (NOS) multibit DAC and replacing my pretty good delta-sigma DAC on the desktop. For the first time in all these years listening to digital, I'm able to totally relax and not hear music files as "digital," just as music. That's kind of priceless...

Hmmmm-- Audio research Ref 6 - wow- Spatial Audio Speakers M3 Triodes--wow-Ref Cd9--Those were the wow times