Ok i pulled the trigger with the HE400i's this is my first pair of planar magnetic cans, my previous headphones were the HD558, Grado SR325e, HE350 Massdrop.
I didn't like the 558's but i loved my Grados, comfort wise they are **** even with G-Cush pads, the HE350 are good Headphones but they lack detail in every area and treble becomes sibilant too early, so i was looking for something not as bright as the HE350, with detail in the treble area, not receded mid range and tight bass, my first concern with the HE400i were the treble, i have seen some people calling them warm, which i don't like, but other people calling them bright to the point they need to mod them, so i was very afraid to make the purchase (here in Colombia there are no "audiophile stores" so audition was out impossible.
Yesterday they arrived the box was impressive to say the least, build quality is good, tho i would liked more metal, then i putted then on my head, they are certainly heavier than the HE350, earpads are obviously better than the cheapo velour of the HE350.
OK now to the point, the sound, i will not go all technical in my experience with the headphones, this is not a review mind you (only one day with them), just my first impressions, my setup consist on a FiioE10K as a DAC, a Little Dot i+ with Voshkod 6ZH1P-EV, to be honest once i putted on my head with some metal i intermediately noticed that they are not as bright as my Grados or my HE350, at first i was quite looking for that increasing the volume, then i noticed everything else, bass is tight, extended and detailed, mid range details are so nice so smooth, treble was not as impressive than my Grados, but i noticed that it was still there but in a different presentation, cymbals were hitting harder than ever, i could hear every detail meanwhile the HE350 give the false impression of detail, sounds stage is smaller than the HE350, but not to the point it worries me (i will play videogames with these), in general i gotta say the HE400i gave me a very nice first impression, in regards to the treble i think my tubes are giving the HE400i's a warmer presentation, i think i will invest on a Magni 2 which is considered a bright amp.
later i will try to elaborate with either a review or a comparison with the SR325e's, HE350's and the Senns HD558's.