I have had 4 DACS and each one has been upgraded at least once. Early on with a modest system and DAC the differences were not as night and day. Of course resolution and detail and less digital glare were what I first noticed. As the DAC's improved the space, airyness ( is that a word?) and instrument definition/locations was better. After that the low frequency presence and clarity was what jumped out. Getting the low frequency cleaned up removed a muddy veil that I had not previously noticed. Then with my last DAC, the background blackness and height and depth of the soundstage and holographic nature stood out and with the upgrade to that DAC it was more Bass note distinction and punch, note decay/timbre, softness and resolution to the higher notes and more background blackness where the music just seems to swell and recede with proper rhythm.
My DACs were a Wyred4Sound DSD DAC2 SE then Schitt Yggdrasil ( I liked the W4S better) then Terminator and Terminator Plus which was better than the W4S ( much better Bass like the W4S had much better Bass than the Yggy, but there was something about it that never sounded right to me and finally a used Lampizator GoldenGate1 that I upgraded to GG3 status several years ago. I am fully satisfied with the GG3 and plan to run it until it fails.