Hi Lucas,
If you have a USB stick plugged in your options for playing music off that stick are on the unit with the stick attached or both that unit and another group of units. You cannot play the music only on another unit that does have the USB attached. To create a group simply click on Edit rooms and groups in the WebUI and then drag and drop the units you wish to group on top of the unit that has the USB stick. Then when you start music playing on that "master" unit it will play on all other units in the group you have created.
Thanks,
Andrew
