BuddyPress.org

Your question is more in line as a support question for the Buddyx theme folks. If you haven’t already tried their support forum for the Buddyx theme.

Furthermore, the first plugin you listed (WP Google Search) provides a search widget that you can add to any of the available widget areas provided by the Buddyx theme, the other plugins you listed may provide a widget as well. This approach might be easier than trying to add relevant code, e.g. a shortcode (if available) to a header file.