I was able to listen to both of these at the headphone festival yesterday. Note, they were among the later things I listened to that day, so my ears were a bit tired by then and I may not have the most accurate impressions. Also, it was a show environment so between the external noise and limited time, I didn't really analyze them too deeply. For reference, they were being driven out of an A&K Kann Ultra.
To me the broad strokes of the frequency response were very similar between both the open and closed back versions. They sounded a bit bass light, but what was there sounded very tight and seemed to extend well. Nothing particularly stood out to me in the midrange response, but they did seem to lean a bit bright, though they were never sibilant. Instead it gave them an airy, almost ethereal feeling. As for the technicalities, they both seemed to display the details of the songs I listened to and both staged very well.
As far as differences, from my short listening session the biggest one was the way they presented the sound. For the closed version, the best way I could describe it was like my head was in the middle of a circle of sound that seemed to have a fairly even sense of width and depth. It even managed to sometimes present certain sounds as coming from behind my ears. While they are indeed a closed back, they don't really isolate like a fully closed headphone and instead sound more semi-closed like an EMU Teak.
For the open back it felt like that circle was just shifted forward. There were even a few times where for a second or two it felt like the sound of an instrument or vocalist was coming from an arms length in front of me. One interesting thing on both versions was that the only thing separating the driver from my ear was a very thin (almost completely see-through) mesh from the pad. There wasn't even any visible dampening on that side of the driver, but who knows what's going on inside those cups.
As for the comfort, these are both excellent. The headband strap that was added eliminated any hotspots on my head and the earpads had plenty of space and were extremely soft. They felt like they just melted onto my head and it felt like I could easily wear these for multiple hours without any discomfort.
My overall feeling of these were that they sounded very light and nimble. Despite the slightly brighter tilt which I'm normally not the biggest fan of, they didn't sound fatiguing in the slightest and actually made for an enjoyable and relaxing listen even with the emphasized top end. Though I would definitely want to give them a longer listen in a quieter space to confirm my initial impressions of the sound.
