Hey Kmcmearty,
Thanks for getting in touch,
Please follow the below steps,
1. Disconnect all USB devices from your MAC.
2. Connect your Allen & Heath Xone:DX
3. Download and install the latest Allen & Heath drivers & firmware.
-- Download Here -->
www.allen-heath.com
-- You will need to enter your personal details at the bottom of that link before the download will start.
-- I have also attached a PDF firmware update guide to help you out.
4. Restart your Mac.
5. Launch ITCH 2.2.2
Does your Allen & Heath Xone:DX now connect with ITCH?
Let me know how you get on :)
Thanks.