Hello Pat,
Whilst I don't have first-hand experience with that particular audio interface, I would expect the process to be as follows:
- Exit Hauptwerk if it's running.
- Install the interface's driver.
- Connect the interface to the computer.
- Launch Hauptwerk. It should report that a new audio device has been found, and then open the "General settings | Audio device ..." screen automatically.
- On that screen, change the "Audio output device" setting to the new audio interface, then OK the screen.
- Load St. Anne's and verify that you can hear its sound through the desired pair of audio outputs on the new interface. If not, and assuming you're just using stereo audio output from Hauptwerk, open the "General settings | Audio mixer" screen, keep the "Master mix 1 ... main/recording" bus entry highlighted in the left-hand list (as it is by default), and in the right-hand pane change its "Audio output device channels: Channels" setting to be the desired pair of the interface's channels. Then verify that you can now hear the organ properly, then OK the screen.