Some interesting suggestions, easo91. Thank you. Perhaps not coincidentally, I also have a compensated graph of the Sony MDR-7506...
And also a comparison plot of the AT M50x, Sony MDR-7506, and a couple other popular closed studio HPs in a similar price-range...
I don't have a graph of the AKG K553 though, MKII or standard. For some reason, nobody likes doing plots of those headphones. I am well-acquainted with the original K553 Pro with the fixed cable though. And have also listened to the MKII version with the detachable mini-XLR cable at GC recently. I have not listened to the Sony MDR-7506 recently though (because GC never has those on their demo display).
Weighted harmonic distortion for the 5 HPs shown on the above graph...
Beyerdynamic DT-770:
https://www.rtings.com/headphones/1-4/graph#440/4029
AudioTechnica M50x:
https://www.rtings.com/headphones/1-4/graph#295/4029
Sony MDR-7506:
https://www.rtings.com/headphones/1-4/graph#386/4029
Sennheiser HD 280 Pro:
https://www.rtings.com/headphones/1-4/graph#299/4029
AKG K371:
https://www.rtings.com/headphones/1-4/graph#1671/4029
Up to $200-250 is okay with me btw, if you have some other suggestions along similar lines. Imo, the M50x and MDR-7506 are probably both a little better at lower volumes, due to the emphasis in the bass and treble. The MDR-7506 appears a little better extended in the bass. And the M50x appears a little a better extended in the treble. Since these are both closed though, some EQ could probably be used to level the playing field a little more between the two, and smooth out a few of the rougher areas on both HPs.
The graphs of the Beyer DT-770 shown above are for the 250 ohm version btw.