Ok, here’s my story in brief:
Set up my Roon Core on a dedicated 2014 Mac mini running Monterey 12.6.3.
Ripped bluray DTS-HD MA 5.1 audio to 48K24bit 5.1 wav files and saved them on the Mac mini internal disc.
Now, using Roon and AirPlaystreaming multichannel audio files to my Yamaha RX-A1060 I only get 2 channel playback. The signal path window says “High quality … Remix channels 5.1 to 2.0… AirPlay streaming”
However… switching from Roon to A*****na and streaming the same files from the same location to my RX-A1060 I get 5.1 surround playback.
Am I doing something wrong or is it a fact that Roon cannot AirPlay multichannel audio to a networked A/V receiver?
Audirvana itself uses Apples System AirPlay it does not have its own code to achieve this. Roon as its mulitplatform has its own AirPlay implementation it does not use system AirPlay so that any os platform the core is on can use AirPlay without this it would be only macs that could AirPlay. This however is relegated to two channel playback not multichannel. Multichannel in Roon is supported via HDMI, possibly USB in some cases or via RAAT over the network to specific multichannel devices. You would need to use hdmi out of the Mac to get this to work.
AirPlay does not support lossless multichannel audio. Not AirPlay nor AirPlay 2, not Apple official implementation nor reverse engineered unofficial implementation. If AirPlay/2 supports any multichannel at all, it would be compressed audio, probably either AAC or Dolby Digital, as passthrough or on the fly encoding at the Apple system level.
As for Audirvana, it most likely is using DLNA/UPnP, which Yamaha supports and allows lossless multichannel audio. Roon categorically does not and will not incorporate DLNA/UPnP.
Thanks for pointing out the difference in my Mac mini / Yamaha RX-A1060 set up: Roon is using AirPlay and Audirvana is using DLNA/UPnP.