I have DT990s and AKG Q701s as well as lower-end AKG K92s (~$40 or so) that I use at work. Have previously had Sennheiser HD555s and some relatively decent AudioTechnicas, plus some other various ones like AKG K81DJ. Have heard DT770s, but don't own them. I've never heard DT880s which are considered to be one of Beyerdynamic's more neutral sounding cans.
I love both my DT990s and my Q701s. I do not find the treble to be fatiguing on either. The Q701s have more treble but much less bass. The treble on my cheaper K92s is worse in quantity and quality than either the DT990 or Q701. I like the treble of the Q701s for speech and certain types of music, but I like the DT990 more for rock/metal music or for movies or games (though I don't use them for movie watching very often). When I go from my Q701s to the 990s I do have to adjust to the lower amount of treble, but it doesn't bother me a lot. My K92s have treble that does kind of bother me (but for the price that's expected). Honestly I think the sound of the DT990 isn't too far off from the HD555 but with better bass, though it's been a few years since I sold the 555s so don't take that opinion too strongly.
I'm not sure what else I can say. I don't find them fatiguing.
I do like bright speakers - my DIY 3-way towers use Vifa XT19 tweeters which are considered by many to be bright. However I am typically sensitive to poor quality crossovers that extend a tweeter to too-low a frequency and/or use too shallow a crossover slope which can cause the treble to be rather shrill. Cheaper Klipsch and Infinity speakers and most car audio setups sound like that to me. Cannot stand those setups. I do not have that problem with any of the headphones above. Not the DT990s, not the Q701s.
If I accidentally stepped on my DT990s and broke them, I would buy another set of DT990s. I absolutely love them. My only complaint about them is that, while they are comfortable when new, the ear pads wore out very quickly and now they rest somewhat on my ears if I don't have them in the perfect spot. Eventually I will get around to replacing the pads. But the padding on my Q701s is much better and is holding up much better. I love the Q701s also and again I like them more than the DT990s for certain material, but overall the DT990 are my favorite headphones I've ever owned.
Last edited by DonoMan; 07-03-2019 at 09:54 AM.