Multiple threading to receive IDOC with SAP Adapter listener


We are receiving IDOCs from SAP using the SAP Adapter listeners. But now, we have some performance issue as there are more and more transactios. And there little space to turning for the single threading. So we want to do it in multiple threads. As I checked, there is always only thread to reveive the IDOCs on the IS, even after I have changed the “Number of Threads” from 2 to 10 on the SAP Adapter listener. So is there a way to let the IS receiving the IDOCs in multiple threads? And what we should to do? Thanks advance for sharing your experience.