Assuming you have no PV in the system you mention (ie it's a Givenergy AC coupled inverter, not a hybrid), then if you add a second Givenergy AC coupled, the two inverters can sit on the same communications bus (Modbus), with one designated as the master and the other as slave device with the EM115 also a slave device on the bus.
If your existing inverter is a hybrid with PV and battery attached, then the diagram linked isn't quite correct as the inverters shown have no battery attached and I wonder if it's to show how an AC-Coupled would be retro-fitted to an existing (eg FIT) system. I know that the Givenergy hybrid inverters need to be the master device for their bus but haven't found a diagram showing any Givenergy AC-coupled devices as slave to a Givenergy hybrid. They show several AC-coupled all working together with one master and a number of slaves but not with a Givenergy Hybrid. I may well be wrong, just not come across a schematic for that specific plant configuration. If you do have a Givenergy Hybrid with PV and battery and are thinking about adding another Givenergy inverter and battery for peak load purposes, then I believe you will have to install a second EM115.