In this version its hard coded to a maximum of 5.
edit admin\includes\functions\extra_functions\multi_xsell.php
around line 237 you will find this code fragment
PHP Code:
array(\'1\', \'2\', \'3\', \'4\', \'5\')
Add as many more as you want.
Also
\includes\languages\english\extra_definitions\YOUR_TEMPLATE\multi_xsell_box_defi nes.php
Add more defines for the additional cross sell headers here
Go to Admin->Configuration->Cross Sell Settings
print this page to save the settings
Go to Admin->Catalog->Multi Cross Sell
Click UnInstall
Upload the 2 edited files
Refresh
Click Install
Go to Admin->Configuration->Cross Sell Settings
Reenter the previous settings
Uninstall the