Ok, it seems my WP-Views plugin was out of date but I wasn't alerted to this via the Dashboard. Strange!
Updated the plugin and I can now set default values for the select boxes when editing the filter controls.
Updated the plugin and I can now set default values for the select boxes when editing the filter controls.
Brings me to a related question though: how can I simply make the pre-selected item the first item on the list (or currently queried item) and remove the ability for the user to search for "all" taxonomies?