You know what guys, I changed my mind again. Somehow the HE400s just have a more realistic timbre than the HE500s. The latter are more pleasing, neutral, transparent, intimate, smooth, and overall higher fidelity, but there's something about the HE400 tonality that gives me goosebumps. Its treble doesn't really work well with female vocals but somehow its mids colouration make them sound startlingly real. Overall it just sounds like such a diamond in the rough.
Excuse me while I listen more on these instead (I've been fiending on the HE500s exclusively for the past couple of weeks).