Tanks philly4, it is setup as you discribe.
After som more testsing i seams like i suffer of som kinde of "silent stream bug".
When i start a longer audio or vidio file the sound apper after a few secons!?
And under this time i can hear "windows sounds". but a short while after i turn of the audio/video file Windows gos silent again?
Exactly same issue here with a NUC5i5RYH and an iiyama B2888UHSU display, but only with displayport version 1.2 (can be changed in the osd menu).
Audio works perfectly normal if I set displayport to version 1.1.
I'll re-check the video driver, but I am not very optimistic so far...
There's a slightly newer general Intel HD 6000 driver available (Intel® Download Center)
However, it doesn't solve the problem.
I had the same issue:
Intel NUC: D54250WYK
Intel Graphics 5000
Connected through DP. Everything looked fine but no sound. Finally did this as a last resort:
Go to Playback devices.
Right mouse on Dell U3415W.
Choose Advanced Tab.
Default format was 16 bit (DVD Quality), changed it to 24Bit Studio Quality and it worked.
Actually changing it to (FM Radio Quality) worked too.
Hope this helps.