I've been using my 10JPNS in the office the past few days. I'm really impressed with them so far. No special burn in procedure, just listening to music on my ipod. No external amp.
In one of my reference recordings/favorite recordings, This One's For Blanton, I noticed faint talking from Duke Ellington in the background in one section. I dont remember ever picking this up with properly amped HD650s before, and I've listened to this album many, many times. Its my favorite album.
So far I think my HD650s go a bit deeper in the bass, and are far more comfortable for long sessions, but I think I may actually prefer the 10JPNs with jazz. The bass is very well controlled straight out of an ipod, which just amazes me, and they are so neutral, but exciting at the same time. I dont know if its the fact that they're closed, or just the drivers, but they seem to offer up more detail and possibly equal the separation of the HD650s I have.
I'm curious to see what they can do with a good dac and amp, but they make the ipod a much more enjoyable source + amp than my HD650s do. I could live with this setup as is for my office. If I were using these as truly portable headphones, I'd skip an amp entirely. The ipod drives them just fine.
I dont know what burn in will do, but I think people tend to get a little to emphatic about its effects. All I know is it sounds terrific straight out of the box.