On Mac/PC open AmpliTube 4 and go to the Settings drop down menu. Select Audio/MIDI set up. Inside here, select the iRig HD 2 for use.
If you're a Windows user, make sure to snag your iRig HD 2
drivers after
registration. Install these, then restart your system. Inside Audio/MIDI Set up you'll see the option for Technology, use ASIO and the iRig Drivers will appear for selection in the Output Device drop down menu.