Volumio can handle multiple devices in order to playback simultaneously the same music source up to 6 rooms (devices) on the same local network.
Go to the SETTINGS menu
Go to SOURCES menu
Make sure the Multiroom Playback is enabled
On the HOME PAGE, click the OUTPUT ZONES icon
Add your devices to the main player to create a group
Every room (device) will have its own volume control
You can create more than 1 group with more than 1 audio source.
Every single group can play different music sources.