Marco,
If I understand you correctly, you want to register two different Event Structures for the same User Event. Here is what you need to do:
Each Event Structure must have its own Event Registration Refnum (ERR). Although this requirement is not strictly enforced by the editor, you may experience strange behavior and hangs if you try to handle the same Event Registration with multiple Event Structures. Next, create an ERR for each Event Structure and wire the same User Event Refnum (UER) into both Register Events nodes. Now, when you fire the user event, it will be enqueued into both Event Queues and can be handled by each Event Structure seperately.
Best of luck,
-Jim