Unfortunetly the latest version of Adapter for NX cannot be configured to generate multi-STEP-file for NX assembly. This function is supported by Adapter for Creo, but why not by Adapter for NX? This function is necessary because:
1. STEP files for a NX assembly are submit to an external manufacturer.
2. STEP files are received by the manufacturer, and check the view of the whole assembly as well as each part by using the set of STEP files.