https://storeus.sonarworks.com/products/reference-4-headphone-edition
This is the best investment you can put into a headphone setup. They have EQ profiles for common pro headphones (including the 880 250ohm premium) and you can load it systemwide (and as a vst on your DAW master) to apply the exactly counter EQ contour to make your headphones as even and rounded (flat, yes, but I stopped using that term because it implies the music would sound lifeless) as possible. Systemwide is super great because I can listen to reference songs on my computer from music players or in the browser, or like play games/movies, and still have the sound correction.
You can also simulate other headphones and stereo systems with their stored profiles, instead of just going flat. And if you personally don't LIKE the completely flat response, you can also apply minor treble and bass adjustments to suit your tastes.
It also has a linear phase option, with some additional latency, to ensure there is absolutely 0 change to the sound outside of the spectrum's range of loudness.
Once I did it for my DT 880's I've sworn never to go back. The difference is actually pretty dramatic; as soon as I toggle the calibration off, the life is sapped out of the mix, the sound of the headphones themselves is pretty tinny and boomy by comparison, and hearing the difference explained basically all of my common mixing mistakes that people point out to me. Weak low mids, excessive bass, harsh upper mids, which were all unknowing compensations for the 880's actual frequency response. Listening to my older stuff on this, it was pretty clear.
Here is the DT 880's average freq response:
As it says in the legend, the BLUE is the headphone's average response, the GREEN is the EQ it applies to counter it, and the PURPLE is the end result (mostly flat, with some bass rolloff that doesn't matter too much in practice, and is necessary because of physics and whatnot).