Ever thought that those hiss and shrill/tizzy treble are not meant to be heard when they were mastered? Reference monitors were used in the mixing and mastering studios, any headphones or speakers that revealed every little noise and mistake on the recordings aren't necessary "better". It's like using a microscope to look at a large format photograph and calling them grainy, most ppl use their eyes to enjoy looking at photographs and not microscopes. To me, the LCD-X sounds very near to studio monitors, if you cannot hear the hiss in a recording with the LCD-X, it's not the headphones' fault, it probably means that the producer or engineer didn't intend for the listeners to hear them in the first place.
What's funny is a agree with your statement, but not in the way you might hope. No engineer, or mastering engineer ever intended for high frequency hiss or shrillness to be in a recording. No one ever intentionally left noise in, that they didn't intend us to hear. Problem is, many studios at the time of all the great western music's production (50's-70's), were unfortunately using top of the line technology FOR THEIR ERA. And certain past era vintage mics, and vintage pre-amps and outboard material, had certain characters each their own, which were good, despite many times being bested by modern stuff with vastly better technical specs in SNR/ETC. But no matter how much beautiful music, with gorgeous natural reverb, and outboard equipment which added a lot of sweetness and 2nd/3rd order harmonic distortion there was back then, that hiss and static and noise and hum was
Even much of what is recorded in the 90's or 00's..... frankly.....sucks in terms of unwanted noise. Modern advantages of high sample rate, extremly low noise recording interfaces with great convertors, and hyper realistic ITB algorithms and plug-ins, which operate at those extremely high sample rates, simply did not exist even 15 years ago.
So to assert that hiss or sibilance, or any other unwanted noise or impurity in any given recording, is somehow a product of any of the mid-fi or summit-fi headphones we have, is foolish in it's premise. The noise is in the recording, bruh. It's there in almost every 20th century recording....and ALOT of it.. Plain and simple, the extremely minimal amount of unwanted noise from Head-Fi'ers post-DA signal chain, including phones, isnt the party at fault.
The inverse, however, can be said with confidence, that house sound sigs like Audeze, since they actively HIDE, and CONCEAL large portions of post-1k audible sound, are at fault, for any unwanted diminishing of the available signal. Because, like the noise, that high frequency signal that can make a track sparkle, or shine, is there. And Audeze and other modern "hi-fi" firms simply veil it much worse than Sennheiser's HD650 ever did.
And even the K812, which I do enjoy a great deal, isn't perfectly natural in this regard. Just like it's closest comparison, the HD-800, it slightly veils some frequency response from 1k-3k, and then has some veiling of commonly unwanted, yet steeply specific "trouble" frequencies EQ'd out of it's high end. Which is why I label, it, as AKG's perfect foray AWAY from true studio reference headphones, and much more TOWARDS the audiophile market. Whereas Audeze just throws an entire gallon of ammonia over all the trouble stain spots, abd douse/gut the high end..........AKG chose, with the flagship K812 PRO, to spot treat each stained spot, which, IMHO, is too smart by half.