try this, add this code to your functions.php file. It will force every link going to photos to go to the slideshow. Note this code will only work if you are not translating the plugin.

function change_link_to_slideshow($link, $page ){
if( $page == 'photos' && is_tax('ims_album') )
$link = dirname( $link ) . '/slideshow';
return $link;
}
add_filter('ims_permalink', 'change_link_to_slideshow', 10, 2);