what is procedure for rendering in assembly
it's up to this matter that what software you have.
in most of rendering motors ,it's possible to rendering assemblies.
but it is important that the software you used it be able to recognizing with assemblies.then u can rendering them easily.
As i know & remember ;solidedge have not a perfect rendering mode.it better to used another rendering software like keyshot.easy to use and perfect in result.and also recognizes with components of your models in design tree and you easily can render all of your components.
i ask in solidedge st6 for rendering after assembly