It looks like eight hall effect ic's , but the picture is blurry, normally four bits would give you up to 16 inputs, so you should be able to decode a binary pattern from them for 8 positions, they may already have pull up resistors, but you may have to reverse engineer the electronics to find out what type of output the sensors have, for interfacing to the opto's.
You would not need to home with this arrangement, with an encoder you would have to.
BTW have you used the Galil general inputs? these can be used on 5v or 24v isolated inputs.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.