As said, SP allows you to import a normal map per project which is you where you get your high-poly detail in.
For your scenario I think you can import the height map image corresponding to your texture (instead of normal map), and plug into the height channel for that layer. SP will automatically generate normals from these and combine it with the main normal map at the time of export (normal,height export are both supported).
If you don’t have height maps for your texture you should be able to convert it in any image editing software (or SD) although I’m not sure whether intricate detail will be fully preserved. In fact someone asked exact question in the SP steam forums (the OP had a large library of normal maps from prior projects that they didn’t want to convert) and I think the conclusion of the thread was that there isn’t a way to use the normal maps directly.