It's a pity there's not a percentage distortion graph in both of the reviews to make it easier to compare, but after taking a bit more effort and comparing the dB differences between the distortion and the fundamental then it really does look like it's a very close race between the headphones and that's whilst the Koss is at around 3dB higher loudness at 1kHz. So in terms of "battle of THD" that was mentioned, then that's a good recommendation because it's significantly less money whilst having an easier & more reliable EQ above 1kHz (less sharp jaggedness).
I agree that the distortion contest will be interesting as it plays out over time. For myself, I have both the LCD-24 and the ESP/95X and measured distortion has not been a factor because ASR-like measures did not exist at the time.
Rather, I opted to use a Stax energizer (SRM-353X or SRM-700T) in place of the E/90x because it is under-powered by comparison; CEE_TEE @Drop stated something to that effect
here.
Later, I substituted an SR-007 MKII in place of the ESP/95X, initially because of the squeaking in the headgear, but over time because I prefer the sound.
That said, ideally, it would have been helpful to use distortion as another variable in the ASR toolkit to facilitate the decisions on the electrostatic gear. Instead, my choices were informed by audiophile opinion and my untrained ears.
Ultimately, to evolve ASR distortion (and other) measures, electrostatics should be included, because it is essential today for a consumer to be able to have the information to make reasonable comparisons between electrostatic HPs (and amps) with dynamic and planar HPs. Especially now that we have companies like Audeze moving into high end electrostatic headphones like
their newly announced CRBN a few minutes ago.
In this example, it is natural for a prospective buyer, like me, to ask how does the LCD-4, or LCD-24 compare with the CRBN? The CRBN works iwth many different energizers including the SRM-700(T|S), so its more complicated than the HP at least for the electrostatics.
Is it reasonable for me to look to ASR to provide the measures and expert judgement to faciliate such a decsion? That is a question only
@amirm can answer. I expect to do so would require a significant uptick in resources and contributions from us as members.