---- DONT WORRY I found It!!! ----
OK for those that cant seem to get this to work or like me had a moment forget-fullness
To get this to work you must have a corresponding Combo Filter in the filter brick for each FK list that you wish to filter on from the menu item
That is: lets say you have a table with 4 FKs something like this
TABLE: My Books[id] [my_book_title] [published_date] [FK=>author_id] [FK=>category_id] [FK=>location_id] [FK=>member_id]
Lets say you have a filter brick with the following combo filters definedAuthors - Categories - Locations - Members
When creating the menu item you can filter on a combination of the four FK lists (Authors - Categories - Locations - Members)
But lets say you create a filter brick for the same table with only two combo filtersWhen creating the menu item you can only filter by location or category
for those of you that are wondering where the code for the modal popup is located
[ROOT]/administrator/components/com_mycomponent/views/fk-field-viewname/tmpl/modal.php
NOTE: If you have changed the name of the FK-table (lets say the fk-table was [categories] and you changed its name to [book_categories])
- you may need to delete the FILTER BRICK (and regenerate) the default admin side collection layout of the view (in this case "my books")
- from my experience if you just delete the filters and not the complete filter brick the respective modal layouts may not be generated correctly
Hope this helps save some time for someone