The CUBE can be configured to play external audio through the CUBE, with the ability to fade out that content whenever messages are assigned to play.
This would be useful if you are using a separate music source, rather than the Channels that are available in CUBE.

To use this functionality, you simply add LineIn to your Schedule, then link that Schedule to a Zone on the CUBE. 

In Primary Settings, there is a volume setting for LineIn. You can adjust the volume of the LineIn in the same manner as the rest of the volume settings (the current setting is shown in the left column. Input your desired setting between 1 and 100 in the right column and click Save).