When building your detail page for a resource board tile, if you use the "download" content type, it displays all of the downloads from the category you select. There is no way to select that you only want to show one specific sub-category from that download category. I am requesting the ability to only show downloads from one specific sub-category. This would have benefits in more than just the resource board area of the site. It would also keep the "Download" section of the "Additional Contents Type" area of the "Content" menu in core from getting filled up with unnecessary and excessive categories.
We tend to build resource-specific download categories. This way we can "add" that category to a particular download file and share it specifically across categories. This also allows us to setup content editor groups by resource tile. Let me know if you need help!