Sure, sorry I forgot about that:
apply_filters('asp_it_query_add_select', '');
apply_filters('asp_it_query_add_join', '');
apply_filters('asp_it_query_add_where', '');Please note that the index table engine uses a completely different query on a different tabe, so to get the fields you need I recommend checking line 350-398 in wp-content/plugins/ajax-search-pro/includes/classes/search/class-asp-search-indextable.php