When you download assets that are designed for Daz you usually get a zip file that starts with "IM000...". Move this to your Daz Install Manager downloads directory (on my pc it is C:\Users\Public\Documents\DAZ 3D\InstallManager\Downloads, but it may be different for you.
Then you can use Daz Install Manager to install the item, it should be listed in the 'Ready to Install' tab.
If you install this way, you should get all the thumbnails etc and you should also be able to use the Smart Content tab in Daz which helps you select the right items for the right 3d models.