ok, well I got it to work, however, its does not work using the file tpl_modules_multi_xsell_products.php

so as a fix, I just included the old file on my server as well solely for cart upsell to use unless someone can work out what the difference is that causes it not to work.

so all I did was specified the table products_xsell1 and made sure I had includes/templates/MY_TEMPLATE/templates/tpl_modules_xsell_products.php

so that when cart upsell calls it here:
PHP Code:
      require($template->get_template_dir('tpl_modules_xsell_products.php', DIR_WS_TEMPLATE, $current_page_base,'templates'). '/' . 'tpl_modules_xsell_products.php');    } 
its works.

like I say, bit of a fudge but I really like cart upsell. :o)