The MEs are designed to be located next to the musician so they can use the physical ME interface to adjust their “mix.” As such, it has stereo outputs designed to be used with headphones/IEM.
If you want to use board I/O for IEM, just use an aux send on the board and skip the ME system altogether.
ME-1 is a receive only device on the DSnake bus, hence cannot send anything anywhere. I can only receive the 40 channels allocated to it by the main mixer.