stepper driver-transformer sizing question

I am a little confused on sizing a transformer to drive some small 30-
Oz-in bi-polar steppers. They are rated at 3 amps/phase 2.1Vdc and
the IMS IB462 drivers I have are good for 12-40V 0-2Amps 160Watts.
What I am thinking is that the motors can take 6 amps (3 per phase).
But can the motors only take 12.6 watts (6A x 2.1Vdc). I would like
to just buy 1 transformer to supply power to 2 or 3 steppers. I am
not looking for high speed mainly low speed high torque. Can someone
help me on sizing the transformer required? Would I also need to run
resistors on series with each driver to limit the current each driver
would be able to recieve?

Thanks
Scott Riddle