I'd definitely say the Audible Illusion 2D preamp I bought in about 1990. I intended to change my system by buying new speakers, BUT...I heard the 2D in my system and it was much bigger change for the better in my system's sound. I kept that preamp for 18 years until I bought a 3A so I could use LO MC cartridges again. After that, it was hearing VMPS 626R speakers in my system--absolutely wonderful sounding. It caused me to want to represent VMPS as a demonstrator for Brian Cheney which I did until his passing. I eventually traded up to VMPS RM40 speakers with most of the upgrades except the OX and still have them.
Your first component that was "special"
I got into hifi 40 years ago. I had a Pioneer receiver, Kenwood table, various entry level cartridges (ADC, Stanton, Empire) and Studio Design speakers. I wound up buying a Shure V15 Type 3 cartridge. That was the first piece of gear I bought that was way beyond ordinary. I had kept the cartridge until about 2o years ago- I sold it because by then no decent replacement stylus was available. Wish I still had it.