Are you sure their Z axis home position is at 8 inches? That doesn't make any sense.
When you are moving the Z axis down, does the Z DRO count down? It should, as that's how 99.9% of people's Z axis work. So you shouldn't need to change the Z direction.
Z Home being zero (top of travel) is the most common, which is why the 2010 macros require it. To prevent the macros from crashing the machine into the top of the travel, it requires the Z Home position to be 0.
IF you go to Config > Home/Limits, Is there a value in the Z Home Offset? If what you are saying is correct, it should be set to 8 there.