If it weren't for absolutely uncomfortable design (too big nozzles, too big body), this would be a decent IEM soundwise - not stellar, but OK.
I literally can't fit these in my ear, no matter what tips and even when I managed to fit them, after a short while, it became really uncomfortable.

I don't recommend these if you can't try them before buying.

Personally, I see as the main issue how boring, unengaging it sounds. I dont really feel like I am in direct contact with the music I am listening. Besides, there is slight muddiness. Still recommendable, but from all the hype for these headphones being recommended everywhere across the internet, I would expect better. I am not keeping these.

In direct comparison with Beyerdynamic DT250, I can immediately tell how much more lively DT250 sounds.
Yes, they are closed and have some issues too, but anyway, in comparison of these two, I really had no urge to switch back to HD600.

Amp used: JDS Atom+

Test gear: PC -> USB to Focusrite audio interface/DAC -> line cable -> Fiio K5 Pro - Beyerdynamic DT250 250ohm/Etymotic ER2SE
also tried: PC -> USB -> Fiio K5 Pro - Beyerdynamic DT250 250ohm/Etymotic ER2SE


The thing is, I compared Fiio back to back with the headphone input on my 20 year old Kenwood home stereo (no high end at all, just a common small, consumer home hifi, albeit a decent sounding one) and the sound was either comparable or even better in overall character on the old Kenwood (!). Yes, Kenwood distorted on high volume, while there was more headroom on Fiio, possibly also details were clearer on Fiio, however I couldn't help to notice that Fiio has some brightness/incoherence in overall sound going on.
Is it a decent amp? Yes, I guess. The sound is okay. Can get plenty loud without apparent distortion. Has nice features, optical input etc., seems well built* , sturdy case and potentiometer,
Will I keep it? No (see the comparison above)

*By the way, when the PC end of the Fiio USB cable makes contact with the metal chassis of my laptop, there is a small sparkling. Seems like something is not entirely allright with the electrical construction in Fiio.

A very nice sounding IEM. Totally recommendable (unless you are a bass-head, need a strong V-shape, or can't tolerate a deep fit construction). The good reputation/hype well deserved. Balanced, clean, euphonic sound.

Positive: Very nice sound overall. Clear, accurate, revealing. Very nice sound especially for being closed headphones - in other words, the nasty closed-headphones congested and plasticky character is not there too much. Nothing distracting in their sound. Balanced. They can handle quite high volumes without distortion. The sound is quite punchy and lively.
For under 100€ these are a VERY good value. Probably very nice value in 150€ range still (but maybe there is something better, I dont know though).

Neutral/possibly negative: Not much sub-bass. But personally I dont care that much. The bass that is there is nice.
Isolation is average, maybe slightly above average (can be good or bad depending on use, I find it to be totally fine).

Negatives:
They suffer from channel imbalance. Its really audible and messes up the whole space perception quite a lot. After googling it appears that it is a widespread issue with this model. I dont know if all DT250s suffer from this or only some (also maybe it was fixed meanwhile...)
But anyway, I find it totally RIDICULOUS. How can a company like Beyerdynamic let this happen??? And especially when it is a model that has been in production for
many years??? Fortunately, the imbalance can be fixed - at least with my DT250s, I managed to fix it to satisfying degree. The problem is actually in the leakage of sound through the connector in the left cup. In other words, unlike the right cup which is closed, the right cup leakes some air and due to that, sound behaves differently in there. I dissasambled the cup and hot-glued over the connector, in a way that it doesnt leak sound. After that, the imbalance significantly improved (its not perfect still, but I notice it only if I pay attention to it).


Comparison: DT250s vs. Audio-technica ATH-T500: No contest really. DT250s are much better in every aspect. The ATH-T500 suffer from nasty congested, nasal, cuppish effect which ruins it. They are quite muddy and harsh.

DT250s vs Sennheiser HD25: DT250s are much more comfortable (obviously though..) and they sound far more natural. HD25s comfort can be improved greatly by using velour pads instead of stock ones, but still its very so-so. But yeah, HD25s are intended for different uses. Anyway, HD25s are too sibilant and their high frequencies just have very weird and annoying character (the main reason I didnt keep them). So, to conclude, if you need headphones like HD25s (for DJing, good sound isolation, portable, etc..) then they are nice, but otherwise, the DT250s sound better. Not as big difference as with ATH-T500s, but still.

CONCLUSION: REALLY GOOD SOUNDING CLOSED BACK HEADPHONES. ONLY IF IT WERENT FOR THAT STUPID CHANNEL IMBALANCE...