I received a file from a supplier that is a STEP assembly of the entire part, with STEP components. I believe it was originally modeled in Fusion 360. 

The goal is to be able to manipulate the assembly and add mates. As is, this is totally impossible. I also cannot open each individual step "component" on its own.

I have tried disabling 3D Interconnect, but this throws an error message and won't load the STEP assembly.

The best I've gotten so far is to import the STEP assembly with 3D Interconnect enabled, and then save the whole assembly as a Parasolid (x_t). I'll then close the file and re-open the parasolid file, which then has each component saved as a .sldprt, which can be opened as individual parts. However, I am still unable to add mates between the different components/solid bodies. It still thinks the entire assembly is a single component. So when I click on the first mating face on a component, it makes the entire rest of the assembly transparent too and doesn't allow mating.

Does anyone have ideas on a solution for this? 

Thanks,

JB