I expected that some of the DVBLink issues reported would indeed be backend related. I am sure they will be able to help you with that on the forum however as we have a lot of Vero 4K users with DVBLink backends that are not experiencing problems.
Stick with SPDIF if you can.
Soundbars can take advantage of 5.1, so with movies and TV shows things will sound better.
Your AML-M8AUDIO.conf is current. I made changes and most people said things were improved (fixed the muddied channels); but a couple of people said it didn’t work for them. As a result, I had to revert things. But I reverted things to July state. Were you watching the same channels / programmes back then?
Running
sudo -s
wget https://raw.githubusercontent.com/osmc/osmc/2b2b23dffcd1967216d79b27bd8a26130546de23/package/vero3-userland-osmc/files/usr/share/alsa/cards/AML-M8AUDIO.conf -O /usr/share/alsa/cards/AML-M8AUDIO.conf
May help. But as we discussed here: September update breaks 5.1 Audio - #4 by john_murray this broke things for you; hence why I reverted things.
Can you also take a quick photo or screenshot of audio settings in Kodi?
If I record BBC1 or ITV 1 News at Six, and output via analogue or SPDIF via 2 channels, will I hear it? If so, I can fix it.
Cheers,
Sam