Add a field to your capacitor table just to the right of the part number, and populate that field with the secondary descriptor. Then use the query tools at the top of the columns to select only the items in a group. The query boxes have a dropdown functionality that is very useful in selecting out major groupings of your parts.
To my knowledge there is no way to add levels to the dxdatabook structure. But, a query dropdown in the table, as I have indicated, is almost equivalent to a secondary level dropdown up at the top. It's actually more powerful, because you can have several of them active at once.