Quick update and a follow on question (probably worth a new thread also).

Just to confirm the 24V wiring solution appears to be functioning correctly on both the e-stop and probe circuits and I can see them functioning/triggered in Mach4 - thanks guys for the reassurance

For the follow on question I haven't got movement yet and I think it has something to do with the PM752 drivers I am using and a lack of Enable connections on those, or it is possibly something in Mach4 related to "Enable" that I am missing, but I'll start a new thread for that...