First of all this should not a debat over MQA.
No, yeah, I just reacted to the most striking thing I saw on the topic since others had already answered your main issue correctly: considering the gear you already have, what you can improve are #1 your headphones, #2 your frequency tuning via EQ.
For #1 I can recommend the same thing I did where after the DT880 I upgraded to an entry-level HiFiMan planar magnetic which was the HE-400i, and got an impressive difference in terms of better imaging, suddenly a depth-axis existing for the soundstage, and better behavior when EQ-ing the bass up (the DT880 didn't give me adequate bass no matter how I tried to push it). Today you could make this transition for even less money as the HE-400SE exists.
But if perfectionism means you're willing to spend substantial amounts and jump straight to what you find recommended as "endgame" gear that could be good enough for the rest of your life, I would have to mention the cheap (depending on second-hand offers) electrostatic system Massdrop x Koss ESP/95X as the best I've heard and my current critical-listening set, or if you don't want to deal with the special energizer I've heard people comparing its capabilities to the likes of the HiFiMan Edition XS, Ananda Stealth or Arya (old or Stealth). In any case, if you like a big soundstage, I absolutely recommend going for tall oval earcups and moving away from circular cups.
For EQ, again if this all means you're willing to spend money for better sound, I don't understand why you're so hung up on the idea of free EQ on PC. You can get 60-band parametric EQ in Neutron Player on Android for only 10 USD or so, and do all the frequency response fine-tuning you could possibly want. The only solution more fine-grained than that would be a convolver, which you can find in Rootless JamesDSP for free (but might not work well with all sound player apps, and requires way more work to create and update tunings).
More software recommendations here:
https://www.audiosciencereview.com/...dows-linux-macos-ios-ipados-and-android.18450