the 990's sound muddy compared to the 400's, and the 990's still sound better. The 400's really sound off to me, and it has to do with their frequency presentation, I've tried playing with EQ to get me through the burn in but it only makes it worse. That's what the 400's sound like to me, good speakers in a terrible listening environment but no matter which way I position them on my head, pressing them against my head, even covering them with my hands, they just don't sound right, they are echoey.
Every once in awhile I find a track that sounds amazing on them, but the overwhelming majority of the songs I've thrown at it would sound better on the 990's. Yes the 400's definitely have a wider soundstage and individual instruments really inhabit their own space but that space is echoey, treble laden, and it sounds live. You might like live sound, I have always preferred the studio albums to the live versions.
I'm really, honestly, hoping beyond hope that it will improve with burn in. These are my first pair of orthodynamic. I've had burn in radically improve cans before. The Q701's sounded like poop out of the box and burn in improved them a lot but never to the point I liked them very much.
I may send them back and get the 650's if this doesn't improve which makes me very sad as I love the concept of orthodynamics and they are as close as my budget is going to get me to something like a ribbon speaker.
Oh one more thing, the cables stab me in the shoulders. The one good thing is after hearing all the horror stories about the cable, I found just a normal, very flexible, grey plastic headphone cable. It's not overly stiff, has a grey/black insulator that is soft and flexible like my Beyerdynamics. They might have improved that.
*To point out the obvious stuff, you should gently pinch the plastic part with the logo, and twist the cups to fit your head (very stiff parts). You should also wear the phones long enough for the pleather to heat up a tad (it is winter where I am), so the memory foam can do its thing. You may need to bend the headband slightly for best fit.
*The frequency response of the phones I will not comment on, as it is a:
*EQ'ing wheen you haven't even spent much time listening (or think you prfer the 990s) makes no sense at all ("to get through burn-in"). The HE-400 seem to disappoint every first-time listener (I was underwhelmed too) - but if you keep em on for a week or so I am sure you'll start to "get it" - then you will want to trim the treble a tad and be talking about dat' bass!
*The HE-400 are unforgiving of
badly recorded music (yes, studio OR live). Echoey-resonant, crappy sounding recording in = Echoey-resonant, crappy sounding music out. Also, the HE-400 are fast, probably faster than anything else you've ever heard, and present a bass response /texture that is brand new to your ears. That takes some getting used to (my old senns, by comparison, are slowwwwwww and bass notes are mud). If you hear crackle, pop, or piercing mids / treble, I will wager $100 that it is partly your music, not your headphones, that are driving you crazy.
*I know nothing of your amp, but I do know the HE-400 benefit from good amps with more than your average amount of iPod / Computer / Cell phone power. The overall bass does firm up.
*I hate the cables too, but aside from re-doing them completely, am stuck with them! But I also have huge shoulders and they don't touch at all. Spend time adjusting head band etc.
*The HD-650s are legendary and much preferred on this site, it seems. But how that would be your next go-to after choosing an HE-400 is beyond me.
*IF you still hate the HE-400s after a week or so, give up, they probably really aren't for you. BUT if you don't, read about the mods / velour pads etc. There are some easy ways to improve on the sound a bit. There are good reasons that these were considered best in their price range a couple years ago.