in the paid version what is a device, is it the device connected to amp/audio system or is the users that stream to the server like mobiles controlling what to stream?
i found nothing about what a user is from these pages only that the normal level has 1 user and the highest level has 6.
a device is the thing on which you install Volumio. so if you take the superstar version, you can install it on 6 different devices, with your account. Say a rPi in the Livingroom, kitchen, attic are 3 devices.