Hi,
I have the same Kind of problem with my Asus-Z87-Plus with Intel Core i7-4770 Processor. The sound works good if I connect only my52 inch Sharp Aquos TV through a Yamaha Amp. HDMI in and out. But when I connect my Monitor on the DVI output, the sound turns off. It comes back on if I diconnect the DVI output.
From what I found on the net, the problem is with the intel driver...
Hope they will find a solution. I had to install my old ATI Radeon HD 4600 card to be able to get the sound to work ok.