bbPress.org

This should work

add_filter( 'bbp_after_get_the_content_parse_args', 'rew_disable_text_editor' );

//editor bbpress
function rew_disable_text_editor( $args = array() ) {
	$args['tinymce'] = true;
	$args['quicktags'] = false;
	if( current_user_can('administrator')) $args['quicktags'] = true;
	return $args;
}

add this to your functions file