I was reading this thread for a long time and when I finished I went to my local music shop to listen to one of these cans. I was listening to HE-4, HE-500, T1, T90, ATH-W1000X, and all I can say is that dr. Fang did a great job in making HE-500, they are wayyyy better than any dynamic headphone. I was really surprised how good they are and how much clarity and details have appeared in my music. I decided to buy them. Previously I had Sennheiser HD 555. I was using them every day for aprox. 5-6h so the only thing I was worried about was weight of the HiFiMan's as I read they can make your neck hurt. Yesterday they finally arrived and my jaw is still laying on the ground. HE-500 is the best headphone I have ever heard. In every song there is something new, something that I haven't heard before. My vocabulary is not enough to fully express what I fell during my listening sessions (btw. sorry for my english ). Also my worries about weight were completely unfounded. I had very long listening sesion just when I got them, 8 hours of continuous playback and I felt nothing. I am wearing them right now and I am barely noticing their presence.
The stock cable is the only thing that needs to be improved. The microphonics is here but I am not moving while I listen so it doesn't matter for me.
Now you probably want to know what amplifier I am using. Here is the part that might be dangerous for many head-fi'ers. Nuforce Icon HDP with 45W PSU. Before you gonna say it is ridiculous to buy so expensive pair of headphones and hook it to something like this read this. I AM ENJOYING THEM VERY MUCH IN THIS CONFIG. VERY MUCH. shout off. I know there are better amps like Lyr or some kind of speaker taps, but the truth is that I don't care. If you are happy with a config you have just be happy and enjoy it. if you are not, go and buy something better.
I agree with you on most counts here. When I had the T1 and the HE-500 I found the T1 to sounds basically like the DT990. It kept most of the good parts, but also kept a lot of the flaws the DT990 has.
I don't think a dynamic headphone really can compare to an orthodynamic headphone. The speed and detail of orthodynamic drivers portrays a certain "realism" that a dynamic driver can never match.