Raspberrypi HDMI audio via ARC

Hi,
I’d like some confirmation whether my idea has any validity. I have both raspberry-pi 3B and 4B units and a small hifi radio which has a HDMI input with ARC support. My idea was to get volumio running on either pi and use is as a spotify remote/AirPlay device. So far I’ve completed the standard installation, ensured that HDMI output device is selected and applied several additional parameters in the userconfig.txt files
hdmi_drive=2
hdmi_group=1
hdmi_mode=16

It’s also worth mentioning that the user manual for the radio specifies that any source device (in this case the raspberry pi) must have an audio output mode of “PCM Stereo” or “Stereo 2.0”. It also mentions that source devices via HDMI must be ARC compliant - which I understand may be the underlying cause, however I’d like to rule out any misconfiguration on my part.

Unfortunately so far I have not been able to get any audio playing via HDMI so far and was wondering whether anyone can indicate where the problem might be. I’d like to avoid buying an additional DAC, from what I’ve been reading so far it should be possible to getting sound going purely over HDMI.

Logs from test playing via spotify and airplay can be found here http://logs.volumio.org/volumio/puqvwad.html. Happy to provide more details or test any theories.

Volumio v3.661

Did you ever figure this out? I have 2 other Pi based Volumios running in the house and I wanted to add a 3rd to our main TV but have the same problem.