I know this is not a Volumio but a hardware feature.
Now that i am enjoying my entire music library over my Volumio player, i would like it if i could hear other sources through it.
I own an TV, with an optical out, i love to hear it over myj Volumio, the same for my BlueRay player.
Does anyone know if there are Raspberry hats capable of just doing that?
Interesting question, I know that the wolfson audio card had such capability… However this is not supported by Volumio unfortunately…
So I think there are no options for you
audiophonics.fr/en/raspberry … 10249.html
Downmix HDMI, but not spdif in.
As most hats are designed for getting music out of the Pi, rather than in, I think you are going to find it difficult to achieve what you are after.