The Sennheiser HD800S is a line extension, meaning the original HD800 will remain in the line, alongside the HD 800S. The retail price of the HD800S has not been announced yet (nor has the release date), but it will include two cables (standard 1/4″ stereo plug and full-size 4-in XLR balanced plug). Also, the color of the HD 800S will be black, both the outer coating and the base material.
Sennheiser let me borrow a pre-production HD800S for a couple of nights in my hotel room (along with a black Sennheiser HDVD800 DAC/amp), and the sense of fullness was improved, and the treble is at least as detailed as the HD800, but with undoubtedly more refinement and smoothness. In my opinion, this is a clear improvement.
Axel Grell confirmed that the tuning has been changed (versus the HD 800). When I asked Axel Grell to describe the changes, he said: “The HD800S is an improved version of the HD800. It has an acoustical absorber like the IE 800, and as a result the frequency response that is more extended, but smoother–fewer peaks. Also, the low-bass is also more extended–not necessarily more bass, but deeper extension.