I like the HE-500 more. It's more refined and precise to me and thanks to planar it's extremely fast. You can listen to Metal or Hardcore, anything. However voices kill the HE-400, the HE-500 is a goddess. It's hard not to hype and not to use pathetic descriptions like this one. :D The only thing the LCD-2 made better for me was the bass (the best I heard) but it has noticably less soundstage and I don't like that at all.
What's the price difference between HE-400 and HE-500 over there (or for you?).