Carrara can see any runtime folder of the poser file structure. You go to the browser window and click on the little arrow over on the right, options appear for linking to a runtime folder. Once linked, you can add content to the folder without re-linking, C6 remembers the file path. You may need to "refresh" the folders before it sees the newer files.
I know that the D/S content downloads in the poser file structure. You may only need to tell C6 where the files reside on your computer. If installing the files into D/S involves altering the file structure, you can re-load the original content into a new external runtime.
There is a DAZ tutorial on external runtimes (intended for poser, but it is the same as what C6 expects to see).