the DRM in hdmi really sucks, but its getting a bit more tolerant.
5 or 10 years ago (back when hdmi was first out) video cards were too strict and the chipsets were, too. if you didn't boot things in the right order, you'd get a race condition. would have to 'reboot the monitor' after the computer started up or you would not get hdmi.
turn off the av receiver and this might turn your tv actually off (switched ac outlet)? that might also cause hdmi to 'go away' and need your pc to be rebooted.
finally all this got worked out, mostly; but I still see remindants of strict drm. I have amazon prime and sometimes I like to fall asleep to a documentary (many of amazon's docs are boring so its a good fit, lol). I start off watching, then I put the stereo on sleep timer and turn the video display off. if amazon is playing at the time, the audio drops out for a few seconds before coming back on again (right after I turn the display off with my remote). at first, I thought there was a bug, but later realized that a few seconds after - the audio came back on. I guess they realized that it WAS a valid use case to 'watch tv' and have the video off (no hdmi link) and yet still let audio thru (spdif out on my win7 htpc).
its getting better but that audio drop out is still annoying and 100% not necessary. sigh.