So I've been listening to the NT-6 Pro for a week now, and burning it in at the same time. I'd say I have around 50 hours on it now, which makes me happy.
If there would be one thing that defines the NT-6 Pro it is CLARITY. These are some of the clearest CIEMs I have ever heard, and that's including the JH13Pro Freqphase. The clarity of these things is off the chart! Every little hit on the cymbals, every pluck of a string on a guitar, every drum hit seems to be so clearly rendered on these things, and I've thrown a lot of musical styles at it as well. Amazing treble and mids also clearly define the NT-6 Pro.
One thing that people may not find so appealing with the NT-6 Pro is the bass. I'd think that many people would be turned off by the seemingly lacking bass, but I honestly like it. There's no thump that accompanies it, as I am accustomed to, anyway, being a huge fan of the MH335DW, JH13Pro, and headphones like the Abyss and the LCD-3. I originally thought this would discourage me from the NT-6s but nope! I'm still listening to it, and still enjoying the heck out of it.
As I'm typing this I'm listening to one of my favorite test tracks, Lazarus A.D.'s "Last Breath", and noting how much of the cymbals I can hear. Some IEMs I've used can't hope to catch up to the speed of the cymbals but the NT-6 can render them so well I seem to wonder how I've never really noticed the cymbals before. Another song I tested these things on is Daft Punk's "Fragments of Time", and it shows how subtle yet clear the bass is on the NT-6. Its so well controlled that I can't help but get lost in the music.
If I was to compare the NT-6 Pro to the JH13FP I'd say the JH13FP is a better all-around CIEM, and one that more people would probably appreciate. If you don't mind slight brightness, and a little coldness, in your sound sig, while looking for clarity and speed, I'd say you're looking for a Hidition NT-6.