I’d say the only piece I bought that I did not consider transformational was the Cary V12 I bought in the eraly summer of ’01. And the reason I say it was probably not transformational is because I was listening to, at the time, a pair of ARC VTM120s, and those amps were kickass! But they were not very reliable, so the Cary was transformational in those regards, because I am no longer gritting my teeth and crossing my fingers when I flip the switches and I no longer keep my soldering iron with a supply of grid resistors next to the amp. Other than that I’d call the V12 a lateral move. Maybe even a hair down, but I wasn’t admitting to that at the time.
When I bought the ARCs they were an upgrade from a Cary SLA70, and that upgrade was transformational. The Cary SLA70 was an upgrade from JVC multichannel integrated, and that was certainly a transformational upgrade.
I went from a B&K digital pre to a second hand modded Cary SLP90, and I found that to be mind blowingly transformational. A couple or so years ago (the years all run together for me post ’17 or ’18) I bought a preowned (from Cary) SLP05, and that was nearly as mindblowingly transformational as the SLP90 was. That SLP05 is good.
I upgraded my 3 piece digital throughout the ’90s and thought it was good but I also thought that it probably wasn’t getting something right. I bought a SACDp (SA10) over three years ago (’20 I think) and I have found SACDs to be transformational as I do not do vinyl.
. . . and on edit: I am currently auditioning/breaking in a speaker upgrade (Revel m126be) from my nearly 30 year old B&W 805s (matrix series). The B&Ws were transformational at the time seeing as how I had been listening to an affordable pair of NHT 2 ways. Some nights I think the Revels are transformational and on other nights I would not go that fra. But they are good.