Well i have had the HE-400 nearly a couple of weeks now and they never cease to amaze me. The presentation, detail and general sound is amazing.
I do have trouble wearing them for extended periods due to the weight and the slightly poorly padded headband though. I tried the HD600 pads + velcro and couldn't get on with it as it padded out the headband enough to result in my earlobes being squished by the cup. I have found a halfway house as comfort is concerned by buying a cheap black flannel, folding it over three times and velcro'ing it to the headband with some success. Still, its a bit ghetto for $400 headphones, there really needs to be a low profile comfort strap for these things.