Xtreme One does not support WordPress Navigation Menu Theme Locations, so it can’t work with UberMenu out of the box. However, it implements a nice hook system, so we can easily remove the default nav system and replace it with UberMenu Easy Integration

1. Add this to the blank child theme’s functions.php:

   function um_override_xtreme_setup_theme_nav() {
       $pri_nav = _xtreme_primary_nav_position();
       remove_action($pri_nav['hook'], '_xtreme_primary_navigation', $pri_nav['priority']);
       add_action($pri_nav['hook'], 'uberMenu_easyIntegrate', $pri_nav['priority']);
   }
   add_action('xtreme_setup_theme', 'um_override_xtreme_setup_theme_nav', 50);
   

2. Activate UberMenu Easy Integration via Appearance > UberMenu > Theme Integration > Easy Integration
3. Activate Strict Mode via Appearance > UberMenu > Theme Integration > Strict Mode
4. In Appearance > Menus, Activate the UberMenu Theme Location by checking the Uber Menu checkbox in the Activate Uber Menu Locations meta box and clicking Save
5. Set your desired menu in the “UberMenu” menu theme location in the Theme Locations meta box and click Save

Note, the UberMenu v3 integration code would look like this:

function um_override_xtreme_setup_theme_nav() {
    $pri_nav = _xtreme_primary_nav_position();
    remove_action($pri_nav['hook'], '_xtreme_primary_navigation', $pri_nav['priority']);
    //add_action($pri_nav['hook'], 'uberMenu_easyIntegrate', $pri_nav['priority']);
    add_action($pri_nav['hook'], 'um_insert_menu', $pri_nav['priority']);
}
function um_insert_menu(){
	ubermenu( 'main' , array( 'theme_location' => 'ubermenu' ) );
}
add_action('xtreme_setup_theme', 'um_override_xtreme_setup_theme_nav', 50);