Well, I traded in my HE-400 for the HE-500 just today. I've been meaning to get the HE-500 for a LONG time, but with the launch of the HE-400, I just couldn't resist to side-track the HE-500. My main concerns with the HE-400 were the mids. I'm very familiar with the HE-500 as i've heard it many times, and because of this knowledge, the HE-400 just seemed under-performing for my tastes. The mids in the HE-500 are just that much more engaging and as an avid Jazz listener, it's hard not to choose the HE-500 over the 400.
Here's what I lost/won with the trade.
+ (because I prefer good news over bad news first): Mids and treble. Simple.
-: Well, bass. The 500 extends deeper and has a more linear response, but the 400 hits harder, and that I like more. Most importantly, $
Neutral: I'm not a huge fan of the cables, but I have new copper hybrids coming on the way so I guess it doesn't matter.
But with that said, the HE-500 is my all-time favorite headphone. The mids are just addicting and it's sheer speed is incredible. Finally, I'm home.
(for the people wondering, I use the Hifiman EF-5 amp with the HE-500 and used it with the HE-400 as well)
Edited by planx - 2/20/13 at 10:13pm