Boy that's super discouraging. That's two bad boards in a row. I used both the default config.g and a config provided by another wanhao user that was linked here. I get sane output from M906 so I guess I won the Duet lottery again.
Your diagnosis seems spot on. The drivers are indeed cold. All steppers are completely idle as if they're not even plugged in.
>>> M906
SENDING:M906
Motor current (mA) - X:855, Y:855, Z:670, E:855:855:855:855:855:855:855, idle factor 30%
Error: Short-to-ground on drivers 0 1 2 3 4
[ERROR] Error: Short-to-ground on drivers 0 1 2 3 4
Error: Over temperature shutdown on drivers 0 1 2 3 4
[ERROR] Error: Over temperature shutdown on drivers 0 1 2 3 4
