Do you have a 32-bit or 64-bit version of Windows 7? I hope it's 64-bit, as there are not any Intel graphics drivers available for Windows7 32-bit, unfortunately. If you are using 64-bit, then perhaps there is some sort of mismatch or corruption in the audio driver. You can try resolving that as follows:
1. Uninstall the graphics and audio drivers, using the instructions at Graphics — Uninstalling the Intel® Graphics Driver and Intel Display/HDMI Audio Driver
2. Restart the computer.
3. Install the latest graphics driver for the Intel NUC (this will ensure the corresponding audio driver is installed too).
I have done a bit of research on the net and came across this:
According to this article dated 30th April 2014, "...HD audio bit streaming works on Linux. It does not on Window though, most likely as an artifact of how Intel structures protected audio playback on the OS, where the Management Engine (ME) is required, but unfortunately the driver will not install".
I have read issues of this on the forum but thought this was to do with windows 8 not windows 7. So is this a general windows issue?