I ordered a pair of these yesterday and they arrived at my house today. My initial impressions are that these things are CLEAR. I listened to one track, and was immediately impressed by how they sound. Certain things are brought forward by these headphones that I missed or were meshed into other sounds by the HE-400 (original). Bass is present, but is punchy and not boomy. For me, it's close to perfect. It's balanced, rather than the approach some headphones go for, which is either anemic or boomy, muddy bass. The HE-400 has more bass, but it's a different variety. Not to say that either is more accurate, but the Edition S goes for clarity, and the HE-400 goes for enjoyability (casual at-home listening).
I enjoy clarity and punchiness, so these are perfect for me. At the moment I only have two other portable headphones to compare to, and both are on-ears. I have the Audio Technica ATH-ES55 and the original Sennheiser Momentum On-Ears. The Audio Technicas, although good, can't compete with either. They sound anemic and lack presence. The Momentums focus on bass. But it's a boomier type. Not Beats style, but more similar to that than it is to the Edition S. The soundstage on the Momentums is almost non-existent, but they do sound good. The Edition S beats it everywhere quite handily. Although it seems unfair to compare the two, the Momentum On-Ears used to retail in the UK for around £170, and the Edition S retails for £190, so it's not as big a gap as it may seem.
I'd be interested in comparing these to something like the NAD HP50, Oppo PM3 etc, but frankly, I'm really happy with the sound quality.
The materials used actually feel surprisingly good. Not as good as my HE-400, but still good. They feel hefty enough, and the clamping force is quite high. All the materials used are matte, which I prefer to glossy.
Once I've had some time with them I'll give a better review.