Just had a thought - there is a program called LPTTEST you can download for free, it tells you what the BoB is sending to the machine, so you will know what pin Estop is on and what state it is in when normal / pressed. Then you will know what to set in Mach. I built a tester some time ago with Leds and an input socket and a output socket - but I can't find it now.

Cheers,

Rob