We've used the NUC5CPYH and NUC3i3's for a while now and had no problems installing embedded 8 on them (though according to the list not supported). Drivers for these are incompatible with the new chipset. Bit strange that intel makes them for win7 but not for win8.
Perhaps the Intel support staff can help with this. However, since Windows 8 is not supported, I would expect to have even more problems with Windows 8 Embedded.
This message was posted on behalf of Intel Corporation
As Al Hill mentioned, Windows® 8 is not supported on that NUC, that is the reason why there are no drivers for window® 8 in the download center with this Intel® NUC Kit NUC6i5SYK.