NAS drive shares (CIFS & NFS) are easily mounted and scanned by Volumio for audio content.
USB hard drives, USB sticks, and use the free space on your SD card for extra or mobile storage.
There are lots of built-in internet web radio streams available, and you can also add your own.
Airplay connection could be a source for Apple devices
DLNA/UpnP is an out-of-the-box option to stream music in hi-res from an external source, using Volumio device as renderer.
FOR PREMIUM USERS:
You can add your own account of Tidal/Qobuz/Hiresaudio.com streaming platforms
You can connect an external digital source via USB port (such digital turntable or CD drive)
You can stream a Bluetooth source
For everyone: Many 3rd party plugins such Spotify, Soundcloud, Youtube and many more are available for free in the PLUGINS section.