Yes, they arrived about a week ago and I've been listening to them every day for an hour or two. Very happy with these headphones, lovely sound all round. Blow my old AKG K701 right out of the water, and they cost about the same when I bought them.
The plugs on the HE-400iare the new 2.5mm type, and there is no back plate as mentioned in the posts above (no need to remove the grills to see this, you can see easily enough while they're still attached). They play surprisingly well straight out of my AK100 Mk2, and the headphone section of my Marantz CD player drives them without any problem. Still, I'm sure they'll sound even better when they have a bit more power behind them.
I have to say I'm less than happy with the Shure SE215-SE iems that I bought this week, but that's another story. Win some lose some!