No HDMI sound

[F0LLETT]

The sound output only works if I use the headphone output, if I use HDMI it doesn't work.

not problem the TV or the cable.

n.b. the same cable connected to a raspberry works for audio.

Did you read whole thread? It clearly states, there is an issue with the linux driver on newer distirbutions, that effects, Raspberry pi also.
I have personally found, it seems to happen on 4k tv's, something to do with when it switches resolution on booting.

[F0LLETT]

I read everything, but it seems that the problem is not considered as it should be.

1 - My old TV is not a 4k but a 1080p (panasonic)
2 - With raspberry with retropie, AGS, RGB-pi the problem doesn't exist.

I report these problems with the A600GS, if you then want to fix them properly otherwise there is no problem.

You're not listening to what I'm saying. Everything you quoted in 2 are using older linux distribution, where issue does not exist (different distro's and drivers).
The issue with no sound on certain TV's needs to be looked at. We are aware and will be looking into it further.