i spent most of the weekend on this issue and it is still unresolved. Firstly, the wifi card is not the issue. I removed it, uninstalled the driver but the issue remained. Also, it now appears that while using it directly with the LG monitor (hdmi to hdmi) there is no issue whatsoever. However, as soon as i use it through the Onkyo 608 (i had incorrectly mentioned 626 in my original post), the video becomes unreliable. It is ok upto booting up to the home screen of Win 8.1 (32 bit) but as soon as i try to navigate around the computer (e.g. go from home screen to the apps page) the picture (through the Epson 8010 projector) goes blank. There is a similar pattern on internet as well. Its ok when i press the home button on the Logitech k400, it goes to the Google page. But as soon as i press any of the book marks, the picture disappears. In one of the related posts, an intel rep had recommended an earlier version of the graphics driver (21 May 14) for someone facing a Onkyo related issue. I have tried that as well but i doesnt work in my case. Please help.
Can you please try updating the BIOS of your NUC? Here you can get the latest version:
As another troubleshooting step, is it possible for you to update the firmware on your Onkyo device? And please let me know the firmware version installed.