Robin,
2.8ohm or 5.6 ohms will not burn the control box. It just mean, that the resistance of motor coil is higher.
Unipolar motors are driven with 4 switches (transistors), while bipolars need H-bridge.
However, those motors at the link you supplied are VERY expensive, and I wander if what you are trying to do is worth it.
What kind of mount do you have? This type of motor is very unusual for any kind of mount that I know of.
BTW, they have 6-wires, so they are unipolar.
To use them as bipolar motors, you have two choices: to use the entire coils (and leave the middle terminal unconnected, this will result in 5.6ohms per coil) or to use half of each coil (middle and one of the end terminals, the other one is then left unconnected) . Either choice is OK and safe to use (as your original motor is 2 ohms), however, you may notice the difference in holding torque, and in 5.6ohms case the maximum speed will be lower (because of higher inductance of the coil). This will probably not be an issue as the motor has gearbox (36 :1) , so the overall torque will be way higher than really needed anyway.
http://en.wikipedia.org/wiki/Stepper_motor