Larry,
It is important to understand that the way you organize your library and the way you organize the DxDatabook database are two separate things, although they are strongly connected and it is much easier if you organize them in the same way,
The tables/entries that show up in the DxDatabook Window, are derived from the DxDatabook database. If you have different tables for the different 'libraries' you want to show in DxDatabook, then you can point directly to the table.
If you have only one or two tables( FC and USL) you have to use queries to get the different categories of components.
In your case I would not change the partitions in the Library (As long as this is fine for you). I would create a DxDatabook database with two tables ( FC and USL), each table carrying the properties that you require.
Then create queries to get the required components out for your DxDatabook libraries and use the queries to create the DxDatabook configuration.
Regards, Charles