I don't know. I liked mine so much that I bought another one for a different room in the house.
An awful lot of people listen at their PCs, I think, so a hardware EQ isn't of any use to them when they can do it just as effectively in software. You get more use out of that feature if you're...
I have a Monolith THX 788 for each of my Sundaras. It's a simple all-in-one package amp/DAC/EQ, and it has the inputs and outputs that work for me. Sounds phenomenal to my ears.
Owning the Sundara is very rational. IIRC, they're the next step up from the HE4XX. Incredible sound for the price, IMO. (With EQ and amp, of course.) Scratch that itch. You may love planar magnetic headphones.
I have a very limited frame of reference, because I've only tried 3 models of headphones, but one thing I can say for sure: the Drop 6XX is overrated to me because they are literally painful to wear. After ~8 weeks of wearing them in, gently bending the metal parts of the headband outward, and...
My wife and I love the Sundara (EQed with the oratory1990 settings for the 2020 revised, with a little more bass than his settings) so much that I ended up buying 3 of them...one for her on the laptop, one for me in the office, and one more in the home theater room. I cannot believe how good...
Depends on the use case, and on how good they sound from that device.
If they can be EQed with an app, that will make a much bigger difference in the way that they sound than buying another DAC/amp.
I've never tried closed-back headphones.
I've only bought 3 models of open back headphones (6XX, X2, Sundara) and I find the Sundara to be the most comfortable. No problems with my glasses, either. My wife tried all three, and came to the same conclusion, so I bought her a Sundara as well.
The X3 got more or less thrashed in the youtube reviews that I watched. I think Zeos gave it the most positive review, but the gist of it was "it barely sounds any better than the X2HR, which is less than half of the price."