I got my replacement HE-400s from Head-Direct on Friday. I have only had limited time with them so far but to the best of my recollection, they sound as they should - like the pair i demoed over the summer. They sound much better than the original pre-order pair i had back in January. They are brighter and more dynamic sounding.
But... They are still a little dark for my tastes. The treble sounds a little peaky - like they are bright in some freqs and recessed in others. The bass is nice and tight and controlled, but they do not go as deep as my MarkL modded Denons. Perhaps my biggest complaint is the mids though. The HE-400s sound a little too warmed over and lush in the mids for me. They are a very mellow sounding headphone that seems a good match for some of my music, but some vocals and middle sounds appear to get a little "boxy" or "nasaly" at times to my ears. The HE-400s, like the other HiFiMAN headphones I've tried, really seem to come alive at higher volumes. This is a negative for me since i cannot/do not listen at high volumes for any length of time any more.
I did remove the grills and listen like that for a while last night and i believe that did open up the sound a little. Unfortunately for the HE-400s, even fully opened up my Denons are more open, clear and airy sounding still. I really have grown to appreciate my D7000's as a result of my recent HiFiMAN trials.
My honest opinion is that they are a very fine sounding headphone considering their price and taken on their own merits - i actually like them a lot more than the HE-500 and HE-5LE. For anyone looking for a do it all headphone in this price range, I consider it the equal to the Sennheiser HD 600 (which i hold in high regard). For me though, my Denons have a very similar frequency range presentation but just do everything better - deeper bass with similar control and definition, clearer and more open sounding mids, and airier treble. I will spend more time over the next week getting to know the HE-400s better, but right now, i don't believe i will be keeping them.