Just out of curiosity, where does the cat 5 ( blue cable above top leds) go? It is saying output on the board silk screen.
Do you know how this machine was able to get ( g ) code? was it manually input via a keyboard? or downloaded via a disk/USB? or was it networked?
Are there any manuals for the servo drivers? Am thinking that it will show in the current config what the output from the board will be step and dir or pwm
when you say you get DRO movement, is that when you push the gantry manually or when you hit the keys in Mach3?
what was the logic for pin out assignment in mack3
Sorry for so many questions and no solution to the problem.

Good luck

Paul