The UX2 will not be detected by the computer until you install the current Line 6 drivers for it:

MAC Drivers : 7.1.3

http://line6.com/software/readeula.html?rid=4321

As for Monkey not being able to connect to our servers, that is a indication that you might have installed a outdated version of the application from a disc.Download and install the latest version from the link below:

MAC Line 6 Monkey 1.51:

http://line6.com/getrelease?rid=4619

Once Line 6 Monkey is installed, remove any additional unnecessary USB and firmware devices from your computer when troubleshooting this issue. Make sure to connect it directly to a USB port and not a USB hub, extension, or keyboard of any kind, preferably connect it to a USB port on the rear of computer. Try using additional USB cables and every USB port available until you are able to launch Line 6 Monkey and detect the device.

After Launching Line 6 Monkey apply any updates that are available until you have a green check next to each component.

Next close all open applications and use the License Manager software to de-authorize and re-authorize your device. Make sure to remove the information when prompted to, and then install again when prompted to, this will ensure that you reinstall all of your available Line 6 assets from your account into your device.