I'm going to cheat a little bit and go back two years since that particular upgrade was my best ever. In 2020 I bought Harbeth 40.2 speakers and realized, for me, focusing on the transducers is the most important part of the audio link. I am no longer fussing with amps, preamps, sources etc. since these speakers sound wonderful on any combination of audio components in my collection.
My biggest upgrade in the last year was to my office system. I had a blue sound player feeding a cheap Emotiva BasX preamp with internal DAC which feeds an NAD 275BEE amplifier connected to B&W 686S2 speakers. I replaced the Emotive preamp with a Topping D30pro. In both configurations I was not using the Bludsound DAC, but rather the Emotive DAC and now the Topping DAC. I realized a very noticeable sound improvement. If I remember the Emotiva preamp was about $300 two or three years ago. The Topping D30pro was $400 this year.
On a side note (FWIW), I can hear no difference between the Topping DAC or the much more expensive, older Bryston BDA-2 when swapped back-and-forth on my main system.
