The 3mf file can contain multiple objects. These objects shall be imported as differend models into S3D. The name of the S3D model can be obtained from the 3mf object.The transformation of the S3D models shall be same as transformation in 3mf file.
In this case an exported assembly from an CAD System can be imported into S3D and the differend models can be printed with differend material. Actually an CAD assembly is imported as only one model.