I'm having this same issue however I didn't update the firmware. I was just playing and it just stopped working with blinking lights.
Over the weekend, i tried to update the unit both method, iphone, ipad and direct USB to computer.
Ipad/iphone said updating but the Bluetooth light would go out on the amplifi and would come back and say failed, device not connected.
USB/Computer stated unit found, updates device, device reboots then its the same result and ABCD blinking lights.
I have tried different computers, different power cord, different outlets and still the same result.
What are my next steps in this matter?