While the M-400 has a built-in Split/Backup port, that port always has fixed port assignments. In order to have miximum flexibility, it's best to use the REAC B Split method of feeding a split location. To do this, connect one of your Stage Units (S-4000S or S-1608) to a gigabit Ethernet switching hub (such as the RSS S-4000SP). Then, connect another switch port to REAC B on your M-400 console. Then, connect another REAC cable to your Split position. You can now go to te REAC B Output Patchbay and patch any 40 sources - Direct Out's, AUXes, Matrices. MONs, MAINs, etc - to any 40 output ports. Those 40 sources can be sent to an S-4000S 0040, to REAC SONAR or to another M-400 console configured as a Monitor/Bcast console. The REAC B Split design provides the most flexibility, assignability and control over any potential Split location.