Newbie stepper kit

[m_c]

If all you want is to move the Z axis manually via the MPG and driver/motor, then what you're looking for is a step multiplier.
It's not something I've looked at for quite some time, but the easiest option is to probably just program an Arduino for the task. Count the pulses from the MPG, then multiply by X and output them.

As for the line driver signals, just connect the - to gnd on the driver, and leave the _ terminals on the MPG disconnected. For something this simple, I wouldn't bother using line drivers, as it'll just add an extra layer of complexity for no practical gain.