Suddenly I found out that my AV8805 was not decoding AC3/DD/DTS anymore playing from my windows 10 pc via HDMI.
It also lost the ability to play higher sample rates!
After a long search and reinstalling almost every involved piece of driver/sw I found out that it was a setting in the Marantz that was causing this.
Its far from trivial that this whould happen, so if you ever come in the same situation this could help you a long search for a solution
This behaviour is caused by having 1 source routed to 2 zones, in my case my PC was routed to HDMI out1 in the "main" zone.
For a test I also needed my PC to send audio to zone2. After that the above behaviour started.
So: dont route AC3/DD/DTS and >48KHz sources to more than one zone at a time..