Well, I've been trying to put in to words my impression of the RE-400s. But I don't think I could do these things justice. I will just say, they are insanely good. They are not "consumer" quality headphones. Meaning, the sound is not colored or tailored to fit specific genres of music. The bass isn't artificially boosted for hip hop and dance music. The mids aren't pumped up to give the impression of clarity. The treble isn't screeching in your ears. They just plain sound,
right. Balanced and accurate and clear.
HiFiMan RE-400 Review - Watch CNET's Video Review
[REVIEW] HifiMan RE400 ‘Waterline’ – The New Reference
These are audiophile-grade, with consumer-grade pricing. The clarity and separation blows everything I've listened to thus far, clear out of the water... With maybe the exception of the Bowers & Wilkins P7. The bass is very tight, if a bit light in the sub-bass. If you want deep pounding bass that drowns out the mids, these are not the IEMs for you.
If you want to hear minute details and clarity, and accurate sound reproduction in live performance recordings, classical, and opera... and still want extremely balanced sound to enjoy more traditional music like hip hop, r&b, rock, and country... You could do a lot worse than these headphones. A lot worse. Even for more money. In some cases, a lot more money.
If you are the type to spend a decent amount of money on headphones, do yourself a favor, spend a little less and try these. They don't have the mass name brand recognition or stylish good looks... But their sound quality can trounce their more famous, better looking, and overpriced competition.