Ahmmm...
You already have optocouplers on the inputs of your BOB. Why would you put another ones?
Figure out the series resistor on the BOB and, if needed, adjust their values to your needs.
It's easy to calculate suitable resistor if you assume that the current through IR diode in optocoupler should be, nominally, 5mA.
Second, check thoroughly your wiring and connections to find "unknown origins" of excessive voltages. OR, place 4-pin DIP sockets on your BOB for optocouplers, for easy replacement when they fail.