You can also add a new folder by right-clicking on the appropriate ... Formats header in the Content Library.

In fact add-ons like Gabi don't ned to be in the same directory tree as the base Genesis any more, though if you use the isntallers theys till require that - DS will scan all the dataDAZ 3dGenesisBase folders it's hooked up to when it loads the figure, this was new in 4.5 or late in 4.0 I think. It's handy when creating add-ons as you can save new morph assets to an empty folder, save any presets there, and place textures, then the whole thing simply needs to be zipped up for distribution without having to separate your files from DAZ' and other merchants'.