Some DACs are USB powered and if connected to a system that is powered on 24/7 means DAC is also on 24/7, which may be not desirable.
On Raspberry Pi model 2,3 or 4, USB ports can be controlled by using uhubctl utility which is standard in Raspbian repositories.
Turning power off is a simple command as:
uhubctl -p 2 -a off
and turning it back on can be done by issuing:
uhubctl -p 2 -a on
It would be really nice if Volumio could embed these 2 commands somewhere in the user interface.
Thanx in advance!