Seriously . . . lots of dead horses at this point.
The HE-400 are (in no particular order):
a) heavier than most phones you are probably used to
*you can loosen the headband, and should twist the cups to fit your dome
b) Sound better with Velour pads than Pleather pads (worth the $10 bucks just to have backups anyway)
*Might sound better with "modded" pads, for which a guide is provided on this forum
c) Do not require, but definitely scale with, quality dedicated amplification (a point of controversy depending on the amp, of course, however great low cost options exist)
d) Do not require, but definitely improve with, Equalizing treble downward (Cut 8 khz and maybe 11 khz by about 3 dB - users preference)
*Also respond extremely well to bass boosting - (maybe 3-6 dB @ 50 hz with a wide "Q" factor, my preference)
e) Have a tendency to "underwhelm" at first listen (subjective comments to follow). After a few days and many hours listening, you are probably either hooked or sending them back. The "sound signature" is described by some as "dark upper mids". But I think that is wrong. would call them brighter and more aggressive than other phones I've heard. The entrepreneur behind them calls them the "JBL or American Sound". That is not a far off comparison because they crank, have a great airy and effortless midrange at times, and stay on the bright side. But the bass puts anything I've heard from JBL to shame, in texture, impact, and extension.
f) Still probably the best headphones money can buy at $400 dollars - and definitely some of the cheapest magnetic planars you'll find!
I love them, recommend them, and use them almost every day. I would buy them again, no question. I personally got really interested because I really wanted to experience a driver technology that I hadn't before. Not sure I can go back from planars - they seem to have some properties that really make the listening experience special.