How to i change to USB audio?

Hey guys.

Im about to purchase one of these Mini displayport + usb audio to HDMI adaptors.

Mini DisplayPort + USB AUDIO to HDMI adapter cable by: Amazon.co.uk: Electronics & Photo

In the product information they say i will need to manually change my audio output to USB in the system preferences.

Does anyone know how to do this?

Once it is connected have a look in Sys Prefs > Sound > Input and select it there.

Cheers for your help

Much appreciated