First up, as you're using Mach with an ESS, you'll only need the single slot (that's unless Warp9 have finally added the multislot capability they've been promising for however many years).

You'll need to add a resistor to the LED supply. You need a voltage of 1.2V at 20mA over the LED, so assuming a 5V supply, you need a 190ohm resistor. I think - I'm a bit tired, and not worked it out for a while! (5-1.2v)/0.02A = 190ohm
Or at 24V, a 1140ohm resistor (1.2K should do)

Do you have the input specs for the BOB?
It may be easier to connect directly to the ESS, as by the looks of your schematic, the inputs are all 24V, so you'd need a buffer board/circuit to boost the sensor output.