TL:DR; Ultimately I feel like these headphones are not worth the $419 I spent on them. There's other products I've spent far less money on that I enjoy far more. I'm a novice so I have a hard time writing in detail about headphones other than "I like it, I don't like it" but here we go. I always end up preferring my Dekoni Blues (primarily for hip-hop and bass heavy genres) or Senn 6XX headphones which were both only $200. If the TR-XOO were sold at the same price I don't think I'd be as disappointed. I've had them for 6 months now.
First of all, these headphones should be sold with a cable that ends in a standard 3.5mm termination. These headphones are very easy to drive and half the time they sound better running straight out of my iPhone 6 rather than through an amp (although it works nicely with my NX3s portable amp and bass boost). If I'm being really cynical, I'd almost think that Massdrop sells it with a 10 foot 1/4in termination to uhhh imply to newbies that they need an amp to go along with these headphones which in my experience is not true at all. I ordered a 4 foot cable with a 3.5mm termination to use instead of the stock. In my opinion, the TR-X00 don't respond much to amplification and they certainly don't "scale up" the way that the 6XX do.
Yes these headphones can rumble fairly well and with EQ you can push the bass pretty far. When it comes to bass extension, they beat out my Dekoni Blues. On the EDM track "Faceless" by Plain Sight, the TR-X00 can pick up some deep, deep rumbles that the Dekoni Blues just kind of pass over. But when listening on the TR-X00 it's like always end up turning up the volume too loud to get the sound I want and when I take them off I realize my ears are kind of ringing, I think it's probably because I end up pushing the treble too loud trying to chase the bass impact. I never have that kind of problem with the Dekoni Blues, they are fun but never unpleasant. One of my favorite tracks right now is the Dillon Francis remix of Cardi B's "I Like It" and I don't know... I just prefer the Dekoni Blues every time over the TR-X00.
The TR-X00 plays rock music pretty well also, heavier tracks like "If You Do, If You Don't" by Cartel or "The More I Sleep The Less I Dream" by We Were Promised Jetpacks sound good. But again, they just aren't preferred over the 6XX or Dekoni Blues. Basically the 6XX are great all-rounders for in my opinion and I just pick the Dekonis when I want more low end, but very rarely do I think "I should grab the Fostex for this track". Honestly even in hip-hop genres I'd still choose the 6XX over the TR-X00 just because they are more pleasant overall.
For reference, my head is larger than average I think. These are pretty unwieldy headphones and not great for on the go. I replaced the stock pads with Dekoni Elite Hybrid pads which are thicker than the original and make it significantly easier to keep these cans on my head. The headband isn't great, but I can wear them for about 2 hours before feeling uncomfortable which seems ok. As I mentioned earlier, these headphones do NOT need an amplifier and run well off a smart phone but for on-the-go listening they just aren't realistic. I'd much rather use one of my IEMs. (Speaking of, my DMGs paired with my NX3s can get some pretty good bass all on it's own at since I only paid $90 for those it feels like much better).
Now there's one area where I do like the TR-X00 and I think that would be called imaging? In the song "Little Taste of Heaven" by Leach there are sound elements that move side to side and the TR-X00 seems to handle that really well. As in, the way those sounds move around my head is quite satisfying in a way that the 6XX and Blues can't match. And while I use my headphones mainly for music, sometimes I do listen to ASMR and I'll say the TR-X00 seems to be good for that. Obviously, I don't really have the vocab to really describe what I'm hearing here but hopefully that makes sense. However considering my other personal dislikes, it doesn't mean much overall.
Conclusion: My biggest gripe with these headphones is when I compare "The amount I spent vs how well I enjoy them" is that I personally don't feel like I'm getting good value for my money. There's other products I've spent far less money on that I enjoy far more. Honestly I'd even reach for my KPH30i before these cans. Maybe I should have done more research but there's only so much I can do when shopping online.
Anyway I seem to be in the minority here and maybe I'll change my mind down the line but as always, maybe someone will find my vague and newbie review helpful :)