I would like to know if it is possible and how to use RPi with Volumio as a sound card for an Android phone cable USB digital source?
Volumio 2
RPi4
AlloBoss1.2
Not sure exactly what you mean here.
The nearest thing I can think of is the usb inputs available with the Superstar MyVolumio subscription … this is aimed at usb turntables etc.
If you gave us more information (how many times do I say that 
) we might understand exactly what you are trying to achieve.
Unfortunately, for now, Volumio does not support Amazon Music HD so my idea was to use the USB output of the smartphone or an Android MediaPlayer to listen to AMHD and maybe see the interface and texts on the TV, transferring the digital audio, to the RPi4 USB for AlloBoss DAC. Something more similar to CD Playback in Sources (already included with Virtuso 
)
Thanks for the reply