Part of the workflow might have to include specific export options before exporting the assembly from Inventor.
I am not familiar with Inventor. As far as AutoCAD, I would first try to BURST the assembly. If the object properties Selection box says "3D Solid (qty)", then you should be able to create your base view. Then GROUP the parts together (as best fits what you are wanting to be visible in the VIEWBASE), so you don't have to select all of the components individually.
It might help to post an assembly here that you export in the same way.