If the Dyn2 requires a 5V control signal for enable, I would run the 7I76 field I/O at 24VDC and instead use some
free 5V step/dir pins for the drive enable (assuming you are not using all 5 axis) This is done by using the GPIO pins:
for example gpio.008 controls the Step04 output (if stepgen 4 is disabled, that is you are only using 4 axis)
Since this is very specific LinuxCNC configuration and setup related, I think you would be better off asking
how to do this on the LinuxCNC forum
Also I seem to recall that the DYN2 enable signal is actually a disable ( enabled when un-driven )
If thats the case you should be able to get machine motion even with it disconnected, and the
alarm output is a nice feature, but will not prevent motion is not connected