Hey Darren,
I think you can limit the Z travel in the Onefinity controller. Since the Onefinity uses stall homing, you could also limit the Z travel by a mechanical obstacle, like shown here for Y axis.
But this problem can be solved without sacrificing Z travel by lifting the Z stepper cage using taller stepper mounting blocks (see pic 2) and extending stepper axle with another coupler. Couplers can be found here.
Another more complicated solution of the same problem was imagined by Bill @Machinist that is shown here where you entirely move the stepper out of the way to get maximum clearance.
For all those who have not yet bought a spindle, it is easier to buy the additional 80 mm mount which avoids this known disadvantage (shown here) because with the 80 mm mount, the spindle clears the stepper cage.