I've heard of one system where the owner rewired his four panels to make the total
output voltage look like just two panels. So, he only needed 2 Enphase inverter units.
You really don't need the EMU, but it's a real nice gizmo to have.
Each of your Enphase inverters has a built-in AC-line communications device.
Each inverter can send it's status info (via 230VAC lines) into the EMU.
That status info tells you how well it's PV panel is working. How many watts it's producing.
The EMU has a network socket that you can plug into your router or directly into your PC.
Allowing you to read-it-yourself, or pay for an on-line
Enlighten monitoring service that will
store status/power history data on-line.
ART TEC - Solar Power - Real Time performance stats
Go down the page and click on '7 Days'.. It's neat software..