Wrote up a review/comparison over on r/headphones of these. Thought I'd post a short version here since these dropped again and some people might be curious about the sound. Sound Overall the sound sticks to that warm, neutralish tone that the rest of the line is famous for. The big change...

I think all my felt, whether adhesive or not, is 1mm.

His was creatology stiffened eco-fi (recycled plastic bottles) but it was 50/50 poly/acrylic where all I could find was the eco-fi 100% poly. Try different things and see what you like best. That's the most important thing at the end of the day. A big part of modding is experimenting and...

Yeah, I'm using some polyester 1mm felt. It's Creatology premium I think, like Solderdude's mod. Cutting a hole in the back defeats the purpose of the mod. That hole is what gives the headphone its bass response. To flatten the midbass, you have to cover it and different materials dampen it more...

I don't think it changes the frequency response at all, but it does kinda feel more open. I'd be willing to bet that could be placebo or expectation bias though. I'm using Scotch permanent double sided tape. Don't worry, it's not permanent except on paper; it holds better than the non permanent...

This is pretty much my impression too. After the felt mod and removing the foam from the grills, I can't decide which is better between this and the 600. The 600 has that perfect emotional realism to the midrange, but the imaging and quickness of the modded 58X really took me aback in a good...

The consensus I've heard from a few places is that it sounds extremely similar to a 660S. I've never heard the 660S myself, just the 600 and 650, but the measurements of the 660 do look similar, at least as far as frequency response goes. The mod I'm talking about is attaching some crafting...

If you're into mods (this one is very easy and reversible), give the felt mod talked about here a try. It takes the midbass hump out completely and adds some clarity and speed to the sound. A great improvement if you find lower end too thick like I do. I still think the 600 sounds a bit more...

I have the Dragonfly 2.0 and I thought it sounded great with the X1. It's not going to change the sound, but it makes the separation a little cleaner and the soundstage is wider. In all honesty though, I wouldn't call it a night and day difference and if you like the way it sounds, I'd just...

Neither have huge soundstage, but the MSR7 has better soundstage and imaging.

Literally any 3.5mm cable.

That's the thing about neutral. Everyone has a different idea of what it is. If you like the Harman curve, the Sennheiser HD6 sound is neutral. If you like the diffuse field, Beyer and AKG are neutral, and then everyone has their own idea of how things should sound. I found the X2 more midbassy...

  The easy answer is "do you have an amp?". If not, the X2 are going to be better. If so, the next question is "do you want a fun sound or a more reference sound?" The X2 is more bassy, the HD650 is also fun, but more neutral and rolled off in the treble. I wouldn't say the bass is bloated...

Pretty much any 3.5mm cable. They all sound about the same.

They're easy to drive, and I don't think there should be any problems from almost any source. Not as easy as a pair of audio technicas, but you're surely fine without needing an amp. I've never heard the HD25-1 ii so I don't know how comparable the sound is.