[Adam Harley (Kawauso)]

Easiest way would be to add <?php $post_forum = bb_get_forum( $bb_post->forum_id ); echo $post_forum->forum_name; ?> inside your theme’s rss2.php, after it says <?php foreach ($posts as $bb_post) : ?>, possibly inside the <title> part.

i.e.

<title><?php post_author(); ?> <?php _e('on')?> "<?php topic_title( $bb_post->topic_id ); ?>" <?php _e('in')?> "<?php $post_forum = bb_get_forum( $bb_post->forum_id ); echo $post_forum->forum_name; ?>"</title>