Microsoft released a Mac Lync client update (14.0.4) in February, 2013 that enables many functions that were previously unavailable with USB devices on Lync for Mac 2011. Please visit http://www.microsoft.com/en-us/download/details.aspx?id=36517 to update your system if you are not running version 14.0.4.
Prior to Mac Lync 14.0.4, if you wanted to use a USB device, you had to first shutdown Lync client, plug in the device and then start Lync. Also, all audio came through the USB device, so you couldn't do split audio that allows alerts (such as your Lync phone's ringer) to come through your computer's speakers while your call audio comes only through your USB device.
Once updated to 14.0.4, you will see a new icon to select/change an audio device from the main window or from a call window as shown below. Split audio also works natively.
CITES has tested multiple Lync optimized and other USB devices and have documented them at https://wiki.cites.uiuc.edu/wiki/x/0y6nBQ. Feel free to add to the list. If you have any issues with the new client, please contact the CITES Help Desk at 217-244-7000 or email@example.com