This is likely an HDMI handshaking issue, and the problem is with the receiver. However, you should know that switching off HDMI devices during playback will mosty often result in a crash of MC, so you're not doing too badly. There are solutions to the problem, but they either require about $100 of hardware, or some time and patience to download software, read up on EDID information and learn how to fool the computer into thinking there is always a Marantz AVR that is on.