HiFiChris posted a review of the Advanced Alpha planar magnetic headphone over on Head-Fi. From the review it sounds like it is generally similar to the HE-400 but with subtle differences.
Pros – •balanced sound
•fast, tight, deep extending bass
•good resolution and separation
Cons – •only a short cable comes included
•some people might find the clamping force a bit strong
•a bit more upper treble linearity wouldn’t hurt
•removing the ear pads, one can accidentally remove the protective mesh in front of the planar driver