Tried this before, but it is not a core audio issue. Instead, there is a deeper issue with Mac and USB peripherals that transcends type of device. There is basically some kind of fundamental flaw in Mac OS when it comes to USB device detection/connection that they never bothered to fix. I have the same issue with USB monitor connections, USB printer connections, USB scanner connections, USB keyboard connections, other types of USB audio devices (MIDI), etc., etc.. I bought my first Mac in 1994 and it had a SCSI connector that worked flawlessly, however, once USB was introduced there was always this same problem across many subsequent generations of Mac computers. It seems to be worse when the computer is frequently disconnected and moved to different environments with different peripherals, but also occurs when the Mac never moves and is always connected to the same USB peripherals. The only solution is unplugging and replugging, and/or cycling power on the connected device(s), and in the worst cases a restart of the computer is needed when it simply refuses to register a USB connection. I often teach in large auditoriums, run events involving many presentations, etc., which usually requires connecting a laptop (often a Mac) to a projector...we always use HDMI in these cases to avoid time-consuming delays/problems in connecting.