Your Enphase inverters require the grid to be live before they'll supply power. Even with your Delta Pro attached, they won't turn on without the grid. There is no way, when the grid is down, to turn the Enphase inverters on even if you were to connect an AC to DC convertor.
The Delta Pro has MC4 connectors so that it can be directly connected to the panels. Using the Enphase micro-inverters disallows you to connect the panels to the Delta Pro.
You could buy more panels and feed them only to the Delta Pro using the DC input and no inverters.