The Issue
In the last year I have posted a few times about HDMI zones not being able to get exclusive multichannel access to HDMI AVRs or pre-pros. I build a new media PC every one to two weeks for people, so I have encountered MC on more different machines (albeit with similar hardware) than most forum members I suspect.
The symptom
When trying to play any multichannel video, the message that "the format is not supported and to try 2 channel 48 KHz} pops up. Therefore, the video file cannot be played in its native capacity. Eschewing WASAPI for Direct Sound works fine, but we all know that that is not optimal quality. All the settings are set correctly, with Windows knowing that the sound device should be open for exclusive access, and is a multichannel device. All connection settings work fine because Win 10's built in video player can actually bitstream lossless formats through them and play the files.
Circumstances of it happening
This can end up happening in any of the following ways:
1. It works fine in my test system, but when it ends up in its final destination, the above issue occurs
2. An HDMI handshake issue or other glitch occurs and then it happens... For one person it was while one track was transitioning to the next.
3. All is well, but then you change a setting in MC (that is not intuitively anything to do with this) and the issue occurs
4. The three known cases were through Datasat, Classe and Anthem AVRs, so not some of the most common brands.
I suspect that at least one instance 3. was precipitated by editing the display device properties in MadVR - e.g. setting that the device connected is an AVR and the connected display is a digital projector. But it is only a suspicion.
Solutions
1. Twice, the problem was solved by restarting the audio service, which I believe resets the HDMI connection and forces a new handshake. Therefore, whatever caused the glitch is removed. However, in some cases that has not worked.
2. Also twice (out of two times), the solution has been to quit wasting time trying everything repeatedly, restarting 100 times in the process, loading new drivers, reinstalling MC etc. Once you make peace with that, simply create a new HDMI zone, configure it exactly as before, and delete the old one. Voila!
I don't recall whether I copied the original zone settings when creating the zone the first time I tried it. The second time, however, I decided to be sure and start from scratch. I think this is the more reliable solution. I will find out for sure later this week, as I am scheduled to fix it for another client, who until now has been forced to have MC open up the Microsoft built-in video player for movies.
This leads me to suspect that something about MC's HDMI zones can lead to corruption of some kind. I have seen this issue 4 times out of maybe 120 systems overall. All that were affected had Gigabyte H270 motherboards and have occurred in the last one year.