Volume locked at 100%

Hi all,
I have just installed Volumio looking for a music server and I am really impressed at first look!
I am nevertheless struggling with an issue that seems to be experienced by some users. None of the solutions solved the problem.
I am running a Raspberry Pi Zero W with a Raspiaudio DAC hat.
The installation and WiFi settings were easy and fast.
The only annoying issue is that the volume control is locked and the mouse turns into a “prohibited” sign.
So the only way of controlling the volume is with the stereo.
Any help?

Navigate to Settings>Playback Options>Volume Options and use Software if your DAC doesn’t have a hardware mixer.

My mistake was that I was convinced my DAC (Raspiaudio) had HW mixer.
Apparently it hasn’t !