The DIM can be an effective download manager.  However, if you are very accustomed to external runtimes, do not let it auto install.  You can disable this by unchecking the install after download box.  If you are archiving, make sure the delete after install is also unchecked.

If you don't have DS installed or don't want your DSON content to get mixed into your DS content.  Make an external runtime folder.  Install the DSON files and the Poser Companion Files to this same runtime.  Make sure in the DSON prefs the DSON is pointing to this folder.