To import PowerGrades, you have to export both a DPX still and the corresponding DRX grade that goes with it. Once you're in a new install of Resolve, you then create a new PowerGrades bin, then right click in the Gallery window and choose "Import," and highlight all the DPX files in the exported stills folder. The DRX corrections will come along with them. As far as I know, it's not possible to import DRX files without a DPX still.
hey John I just got around this issue by clicking option button in the bottom left corner when choosing while file to import. It will give you the option to highlight drx files and you can then import a drx file without a dpx file linked to it