In the tpl_checkout_confirmation_default.php you will find the line:
Code:
          <td  class="cartQuantity"><?php echo $order->products[$i]['qty']; ?>&nbsp;x</td>
You could alter that based on the products_id quantity doing a look up of what the current products_quantity is:
zen_products_lookup($order->products[$i]['id'], products_quantity)

and based on the results add something to that code that displays the quantity being purchased ...