As an update to listening impressions I noted this on the JH13 thread as well.
I am finding that the Shadow works very, very well with the JH13's. You get a deep resounding bass, that I do not get even on my modified iRiver when using just it as a player and amp. The iRiver modified is excellent sounding and is a pleasure with the 13's but I am surprised at the deeper bass from the Shadow, more separation and greater precision of local.
I know that some have stated that they don't hear much if any difference with amplification or not when using the JH13 Pro but frankly I do. It can be good or bad and is a tribute to how easy the JH13's are to drive but as with any fine driver, the better the amplification the better the sound, provided you have a good source to begin with. I use lossless, CD or WAV for my listening. Most of the time it is the optical out of the iRiver H140 or H120 (140 with a 120gb drive and the 120 with a 80gb drive) to the iBasso D10 with the line out of the iBasso, which provides the dac.