You will need to use a USB hub between the AudioBox and your USB C Adapter.
From our own testing and understanding of the devices and technology at hand, "any" common consumer grade powered USB hub will suffice. Sabrent, IOgear, Anchor, etc... are all common brands you can find most anywhere.
In a nut shell, the AudioBox USB is classed as a USB 1.1 gen device.
MacBook Pro's are classed as USB C or 3.1 gen device.
USB C is "backwards" compatible with early gen USB devices, but this will never guarantee that they will work "well". Audio streaming devices are also more involved.
So, when you connect a powered USB hub to the new MacBook Pros, it will effectively communicate 1st gen devices with new gen devices.
If the issue remains, please create a ticket to technical support.
Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new