I have the same problem.
I was able to get Windows 7 x64 working on the NUC6i5SYH.
- NUC6i5 has four external USB 3.0 ports and two internal USB 2.0 ports. The internal ports require a non standard 4x1.25 mm header to USB adapter. You can purchase it here:USB A Female to 1 X 4 Pin Internal USB Connector 1.25 mm Pitch
- Windows 7 doesn't support USB 3.0 on the installation disks. Therefore, you cannot use a USB mouse or keyboard during installation.
- You need to transfer the Windows 7 installation to a bootable USB drive. I had to download the Windows 7 SP1 ISO. Creating an ISO from the DVD would not work with the USB/DVD Download Tool.
- You need to add the USB 3.0 drivers to the installation. This involves downloading the USB 3.0 drivers from Intel. Windows 7 also did not trust the files and you need to unblock them. You then need to use the Deployment Image Servicing and Management Tool and modify the boot.wim and install.wim file to the SOURCES folder on the USB install drive.
- Once Windows is installed, the Windows Update will NOT UPDATE. You need to download/run the KB 947821: System Update Readiness tool
I followed links 1 and 2 and got Windows 7 x64 installed. There is a Windows 7 USB 3.0 Creator Utility, but this doesn't work with the NUC6. You have to do the full installation of Link 1 with the unblocking of link 2 on the USB 3.0 driver directory before you copy the to the wim folder.
It took about an hour for the System Update Readiness Tool for fix the operating system to do updates.
Hope this helps...
Nice to hear you fixed your computer issue.
I solved the Problem this way without installing USB 2.0 cables:
- Download Win 7 USB 3.0 Driver Download USB 3.0 Driver: Intel® USB 3.0 eXtensible Host Controller Driver for Intel® 7 Series/C216 Chipset Family
- Unzip driverpackage, extract directories "HCSwitch" and "Win7"
- Follow these instructions: http://translate.google.com/translate?sl=de&tl=en&u=http%3A%2F%2Fwww.com-magazin.de%2Fpraxis%2Fwindows-7%2Fwindows-master-stick-88196.html
- At "download drivers" section you only have to integrate the two drivers from step 2 into the two (boot and install) WIM images, don't install the Bittorrent client
- Finish the images and install Windows 7 from USB
- Windows Update probably won't work, fix it with: https://support.microsoft.com/en-us/kb/947821
Then it's also possible to upgrade to Windows 10.
Thank you for sharing this information.