Hi Maxmachine,
assigning the eXtro BGS module to only some menu items is possible, since this is a Joomla default feature. We've tested this behaviour and it worked as expected.
Example:
Let's say you have 3 menu items : Home, News and About , and you want the eXtro BGS only to appear on Home and About, but not on News, then you should do the following:
In the module configuration, click on 'Menu Assignment' and select 'Only on the pages selected' from the select box. Now you'll see all your menu items listed, and you can tick on which ones the module should be displayed. In the example (if you only want Home and About to display the module), you should therefore tick 'Home' and 'About' and unselect all others.
I hope this makes things a bit clearer.
maike