I'm very interested in the absolutely most non-fatiguing high end headphone. Stax, dynamic, orthos?
I believe LCD-2 will have the least and smoothest treble of the high-end headphones, if treble is what you're worried about. Rev. 1 in particular. You can probably grab a used one from someone "upgrading" to rev. 2.
I find the HD800 fatiguing in treble, and the LCD-2 (rev. 1) fatiguing in bass (although keep in mind I do listen to a lot of electronic music and generally listen at relatively high volumes). For those reasons, I frequently switch from one to the other. Of course, volume level is extremely important. I had a GS1000i for a couple weeks and remember it being non-fatiguing, particularly because it has a low volume specialty and I would listen to it at lower volumes.
I actually found that with specific cables, amps and sources you can make the HD-650 quite fatiguing! Yes, it's true..and they say you can't change a headphone's signature
Most non-fatiguing is the HD-600 with it's stock CABLE only IMO. This headphone would be perfect for falling asleep with. More so than the HD-598.
I actually find the HD-600 less fatiguing than the HD-650 somehow.
The most fatiguing is the Grado SR-325i to me. I was younger when I first heard it and I'm been afraid of Grado after that. Lately the 225i has interested me, but maybe the HF-2 would be a better place to start.
The 325i to me was like someone banging pots and pans in my ears. One of the rare headphones that disgusted me. What's sad is that it was my first really expensive headphone purchase.
OP, you'll get a heap of idiosyncratic views here, but if you're looking for the concensus view, it's that the HD650 is generally the most unfatiguing in the lower price bracket, and the LCD-2 (Rev1) in the higher. These are phones whose treble is pitched at what I consider a "natural" level but some others consider a litle dark, or shelved. The LCD-2 is particularly unfatiguing as it's just so balanced and low distortion and never seems stressed. It is however heavy, so I guess you could say it's fatiguing in that sense. The HD650 is extremely comfortable.
is it just me or do your ears "get in shape" as it were?
like when i first got my Beyerdynamics i found them fatiguing but after a week of good listening no longer would i get that tired sharp kinda annoying pain deep in my ear
Yes, you definitely get used to a headphone. Personally I think that's why so many people experience burn-in.
Some people are sensitive to bright treble though, or have tinnitus. And if a headphone is too bright or too bassy you're going to get headaches so fast it'll be hard to get used to it.
There is no absolute answer to that question, it varies a lot from one user to the next. Some people swear by Stax but those I had annoyed me after an hour or so and that is the reason I had to get rid of them. Besides that, the sound was too "airy", diffused. Not saying Stax are not great, just not great for me. So far of all the headphones I have tried the less fatiguing are the HD 600/650. My RS1i's are also quite comfortable provided I use the flared pads but the twisting, heavy cable becomes a nuisance after a while.
L3000, K340, W10VTGs would be my picks for non-fatiguing headphones (though apparently there is a bit of SQ variation with the latter two, I've seen folks describe the K340 and VTGs as bright whereas my pairs are anything but). The HD650 is another headphone with a great deal of variation between pairs, the older pair I had sounded quite dark and the newer pair was the single most fatiguing headphone I've ever owned, they had a peak in the upper treble which I found almost unbearable. The K701, W1000, and HF-2 (probably the brightest headphones I've owned) all were much less fatiguing than the "new" HD650 for me. I haven't heard the LCD2 yet sadly.