If you've already added this activity, just select it on the 'Activities' page and delete it (click on the trashcan). Then select 'Add Activity'.
When it prompts you for 'Type of Activity', click 'Listen to Music'.
When it prompts you for subcategories, select the one that makes sense - e.g. 'Listen to Radio (AV Receiver, Tuner)' instead of 'Listen to Music (Digital Cable, Satellite TV).
When you finish the setup, it will only prompt you for which receiver to use (if you have more than one under devices).
When it prompts you for 'Type of Activity', click 'Listen to Music'.
When it prompts you for subcategories, select the one that makes sense - e.g. 'Listen to Radio (AV Receiver, Tuner)' instead of 'Listen to Music (Digital Cable, Satellite TV).
When you finish the setup, it will only prompt you for which receiver to use (if you have more than one under devices).