I found where symbols are pulled from. You use <Setup><Settings...>(Symbol Libraries) and define a path to a folder ABOVE the folder with the symbols for a Table in the database ('.\my_library\Diodes' for example). You then need a folder in that folder called SYM ('.\my_library\Diodes\SYM') and then the symbols need to be located in that folder ('.\my_library\Diodes\SYM\1n4001.1', etc.).
A couple handy commands from the DxDatabook window are:
<right-click><Configure>(Rescan Symbol Libraries) and
<right-click><Configure><Edit Configuration>(Update All)