How to handle low voltage stepper motors?
1) For low performance applications, you drive a stepper motor at its rated voltage.

For high performance (higher speed) applications, you use a higher voltage with some form of current limiting. This allows the current to change faster in the inductance of the windings. 

2) The simplest way is to use a high voltage drive, with series resistors. The resistors will get hot, and must be sized properly.

3) A better way is to use a current source drive. The old skool way of doing this was with linear current sources, which will get hot, and must be sized properly.

4) The best way to drive stepper motors for high performance these days is to use a buck SMPS driver set to deliver constant current output.