I have read your post 4 times and don't understand the problem. Either it is very simple using a List or requires a table to assign values.
Please give a more detailed example.
If the checkboxes are "A", "B", "C", the values to assign are the letters "A", "B", "C", not a number. Other software does this differently, but in FileMaker, the visible value is what is stored in the field.