First of all, the big question for stepper motors: it's bipolar, unipolar or configurable?
It depends on how many wires it has. A 5-wire motor can't be used with that driver. A 4-, 6- or (rarely)8- wire motor can. The KH56 is a 6-wire motor so it can be used in bipolar configuration.
As for the current rating: the stepper motor (especially in bipolar mode) is usually driven with a constant current, not with a given voltage. For that kind of motor you could either:
Simply apply the rated voltage (1.76V) to the winding, in which case it will consume about 2A, or
Apply a current of 2A and keep that regulated, which is the approach followed by drivers.
This is the per phase current rating.
The motor has two coils in quadrature so you will have a total of maximum 4A flowing in the windings. This is the whole motor current rating.
However this doesn't mean that you need 4A on you 12V power rail.
The motor driver is more or less a switching converter. It only gives pulses of current to keep the magnetic field charged; you can see the current ripple in figure 9 in the datasheet, for example.
In short, you program the driver for a given current (with a resistor, in this case) and it regulates it but it's better if you think of it as power. About 2A at 2A are 4W, so it's an 8W motor. At 12V it's somewhat less of 700mA.
By the way circuit layout with the TI stepper drivers is quite critical; do it exactly as it is shown in the datasheet. Obey the recommendations on capacitors, they are quite important, too.
