The two pins pretty much tells the machine that there is a cap on the end of the torch and it is ok to fire the torch.
As far as a thc. There are only 4 inputs on the breakout board (bob) which you will need to add in, so choose your thc wisely. Let’s say you did the proma thc 150. You send two signals to the bob, up and down. The proma thc also has arc ok signal which tells mach it’s ok to move. Now you are left with 1 input which I would suggest to use as a probe input for z axis touch off for initial height.
You could use the the proma thc sd which intercepts the signal to the z axis stepper driver and doesn’t send any signals to the bob. I think this would be the way to go with the current bob. Your plasma machine may have the option to send an arc ok signal directly to bob and now you have 3 inputs left for other things, z axis probe, e-stop, limit switch, etc.
Also you will need to modify your bob and mach to accept inputs, which I describe here
Just my two cents.