Flatpak multichannel audio over HDMI

I've recently started using the LE13 nighties on an intel NUC. All the HDMI audio works great in Kodi but apps/add-ons running via Flatpak are limited to stereo and i'm trying to use Moonlight with 5.1 surround.

I've tried tweaking the custom audio device setting in "External programs helper" but i don't think that's where the problem is.

I've added some Pulseaudio daemon config with "default-sample-channels = 6" which did make it start outputting 5.1 but the channel map is all mixed up with audio coming from the wrong speaker. Changing "default-channel-map" in the same config doesn't help.

Anyone have any ideas? it would be really good if this could be streamlined / automatically configured based of the Kodi audio output settings in future.

Interesting thanks, speaker-test works correctly, lists the expected channels and the tones play from the expected speaker.

LibreELEC:~ # speaker-test -Dhdmi:CARD=PCH,DEV=0 -c6

speaker-test 1.2.16

Playback device is hdmi:CARD=PCH,DEV=0
Stream parameters are 48000Hz, S16_LE, 6 channels
Using 16 octaves of pink noise
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 22 to 349525
Period size range from 11 to 174762
Periods = 4
was set period_size = 12000
was set buffer_size = 48000
 0 - Front Left
 4 - Front Center
 1 - Front Right
 3 - Rear Right
 2 - Rear Left
 5 - LFE

But when I config the pulseaudio to with "default-sample-channels = 6" i get:

LibreELEC:~/.config/pulse-daemon.conf.d # pactl info
Server String: /var/run/pulse/native
Library Protocol Version: 35
Server Protocol Version: 35
Is Local: yes
Client Index: 0
Tile Size: 65472
User Name: root
Host Name: LibreELEC
Server Name: pulseaudio
Server Version: 17.0
Default Sample Specification: s16le 6ch 44100Hz
Default Channel Map: front-left,front-left-of-center,front-center,front-right,front-right-of-center,rear-center
Default Sink: auto_null
Default Source: auto_null.monitor
Cookie: b3b3:64ec

I know pulse is used for Bluetooth audio and that's limited to stereo, maybe some existing config for is getting in the way.

I tried a "default-channel-map" like you suggested in the daemon config, same place I set "default-sample-channels = 6" but it had no effect.

Most other suggestions online talk about editing /etc/pulse/default.pa which is read only for us.