I got a pair of the HE-400's when they were on sale around BF, wasn't particularly impressed with them though. I think they are a bit over-hyped. A lot of my favorite vocal selections sound recessed.
As a long time user of the HE-400's all I can say is this is a STEAL.
Get the velour headpads and the cushioned head band and you'll be in for one nice comfortable set of cans.
However some warning , these get a bit "warm" due to the large magnets so if you sweat this is a consideration. Also despite the low power requirements (on the HE-400's) it doesn't change the fact that the HE-400's and 500's are planar magnetic. A headphone amp is really required to bring out the most in both. A good entry level headphone amp is the Schiit Magni.