Isolated sound card requires Pi kernel version 5.4.58 or later

The mute problem will be solved when the Volumio kernel becomes 5.4.58 or newer. I understand.
If the relay turns on normally, there is no problem with continuous playback.

Yes, for sample rate issues, playback options, you recommended
I saved it with changes and checked the playback sound.

Audio Resampling: On
Target Sample Rate: 96KHz
Resampling Algorithm Quality: Very high

Hi, IMHO there is a new addition you can make to the configuration of the DAC to make it work with curerent kernel (5.x won’t come soon, too unstable at the moment).
See for example this commit:

Darmur added a script to initialize the DAC. You can do the same to mobprobe the module you need

Rasbian ships with kernel version 5.4.xx right now. It is more outdated and unstable to be on a less progressive 4.19.xxx kernel.

I am concerned that this mute bug fix I submitted to the Pi’s Linux kernel is not in the current Volumio kernel … if that is the case, the Volumio kernel is more then 3 months old.

We prefer to have stability rather than being cutting edge.
Kernel updates usually break lot of stuff, especially i2s DACs, so we want to be 100% sure that everything works when upgrading. We can’t just upgrade for your DAC, risking to break support for other DACs. From our latest tests 5.xx was breaking quite some stuff.
I suggest to apply the fix I suggested

You can add updated modules or missing modules if required

As @volumio mentioned, you can also add a custom script

I have opened a pull request to autoload the necessary module :