There's a question that needs be answered before we can fully solve this, but first some background on a check box formatted field:
When you click two or more items in a check box value list, all such values are stored in the same field separated by carriage returns. The items will be listed in the field in the order in which they were selected by the user not the order shown in the value list.
Example, let's say you have a check box formatted field listing [ ]red [ ]blue [ ]yellow.
If a user clicks "blue" then "red", the values are stored as
Now the question:
Let's say a user selects 3 items for their report. Are you wanting to find all records with item 1 AND item 2 AND item 3? Or do you want all items with item 1 OR item 2 OR item 3?
It may clarify things to post an example with actual values to illustrate what you want here as there could be additional issues involved in setting up the correct find request(s).