AC coupling is connecting a grid injection inverter on the AC output—that you cannot do. The AC output is unidirectional, it is only for providing power to loads. It cannot accept power from a grid-connected inverter. If you wish to increase the PV capacity then either add another Any-Grid PSW-H in parallel (you may disable the AC load output and use it purely as an MPPT charge controller on the same battery) or use a separate MPPT DC charge controller in parallel to the Any-Grid PSW-H on the same battery.
