I got more than 6 posts working by commenting out two lines in inc/featured-content.php – lines 154 and 190.
// $featured_ids = get_transient( 'featured_content_ids' );
// set_transient( 'featured_content_ids', $featured_ids );
You also need to increase quantity on line 475 of that file. I also made the change pointed out in the first post here.
