I've read your comments - and in short I get it.
Even as a staunch supporter of "non-audiophile" electronics (like good laptops), I have no question that maximum performance of the HE-400 is somewhat source dependent/recording/amp dependent. There are still people that hype too much <cough earpads and 10 watt amps>, but the HE-400 definitely have scaled for me. They do need a little more power than the typical headphone (not much more), and a great source to sound their best.
As for soundstaging arguments, I am listening to that with interest. For me, the headphone 'sound' has in general been a little too L/Channel R/Channel sounding lately. It is occasionally preventing me from getting lost in my tunes, but this is more a headphone problem than an HE-400 problem.
Do you use crossfeed? That helps a lot for me. In terms of a realistic soundstage from headphones, the HD598 has the best so far for me. The Audio Technicas are the most dramatic, but not necessarily realistic. The HE-400 is... Adequate as I've said before. But also tends to remind me more of a closed headphone than an open one.