500 vs 6 SE, some more thoughts:
My parametric EQ settings aim at the places in the treble where there is ringing, and if not ringing per se, then behavior that does not make that threshold, but the membrane has not stopped moving. 3-3.5k, 9k for sure. 6k a bit. It has to be parametric, and the Q has to be high (narrow), and the db cut enough to cut the ringing, but not so much as to hurt the music. Plus there are adjacent areas in the treble that need to be boosted too, so narrow, and please don't try fine tuning this w/o a regular fixed freq EQ - even a 31 band on both channels won't do the job, never mind the newly popular ones with 4 or 6.
Over time, HFM has tuned their leading round cup headphones to have less and less of that ringing. The 5LE > OG 6 6 screw > 500 > 6 SE > 6 SE v2 (by ear). The unit to unit variation was higher earlier, but becoming less due to improvements in manufacturing (the driver, let's leave all the other bits outside of that). On my set-up of the past few years, with some EQ of those hotter spots of the 500 and 6 SE along with basically the same mods, they sound more alike to each other than stock, but not the same, and never will be. Someone said that if you take the extra glue off of the driver edges of the SE's, they do bass impact like the 6 screw - and would doubtless ring more.
Of all the technologies I know to create sound, planars have the biggest issues with the stopping of the membrane. Ribbons and estats have the least (and move the least, so thats why intense impactful bass isn't usually a strong suit with them). Planars have an excellent leading edge and that's what catches the ear. And the true ribbon Maggies, with the Maggie or other subs hide their issues pretty well, but full range headphones? Not so much. Horns and folded ribbons are good at stopping too. Dynamics have a lot of years and money put into them, so some of the good ones behave well too. However, make the Q too high, and put backs on them, and you have the bass cannons - usually with V shapes that bear little consideration as accurate transducers (yep another cheap shot at rotten fidelity).