Are those new 400s the blue ones? I saw that preorder thread over at head-fi.org, I think. I found it interesting that those had a higher sensitivity and are apparently much easier to drive, whereas other planar headphones I've read about tend to be very difficult to drive. What amp are you using? I'm planning to order a Meier Corda Jazz in the next week or two, so I'm pretty excited to see what cans sound best with it.