How does it work the Digital and Analog Inputs Playback feature?
Volumio handles external digital sources processing them and converting them to analog with the Volumio’s connected DAC
Connect any USB or I2S input (such as a USB turntable, a CD-drive, an USB audioboard or the Hifiberry DAC Plus ADC I2S DAC),
Play the input on Volumio
You will find the external sources between the BROWSE PAGE sources
Click on that icon to enable the input signal
Here the video tutorial:How to play an external digital audio source? [Digital audio input feature]