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The Xylotex can only supply 2.5amps. Here's some info from their data sheets.
Unipolar Motor Note:
When Setting Vref for a UNIPOLAR rated motor, use a current of 50.0% of the rated unipolar current, when wired for series mode. EX: Unipolar rated at 2.0A, when wired in series mode would be setup for 1.00A, or Vref of 1.44 Volts. Half winding mode would use the full 2.0A rating, Vref = 2.44V.
The drive will work with three type of stepper motors, 4-wire, 6-wire or 8-wire motors. 4-wire motors are truly bipolar, and can only be run as such.
6-wire motors can be wired two ways to work with the bipolar drive.
The first is half-winding. In this method, one end wire, and the center-tap wire of the phase is used. The other end is insulated and left unused. This method uses unipolar nameplate current specifications, and will produce nameplate torque.
The second is series winding. In this configuration, the center-tap is insulated, and unused. This method uses all of the wiring per phase, but has double the number of wire turns as half-winding or unipolar mode. Because of this, the amperage requirement becomes half the nameplate rating. Because the wire in the coil can handle more current than ‘half’, motor manufacturers will often “boost” the torque rating by specifying currents up to 71% of unipolar rated current while running in series mode. This is fine for FULL step motor drives, but not necessarily so good for microstepping drives. Using this much can smear microstepping smoothness and accuracy. Any extra torque achieved by this method will generally be lost to machine vibrations due to loss of microstepping smoothness. The best performance will be somewhere between the 50% and 71% current rating.
The advantage of using series winding is that lower power drives may be used. For example a unipolar motor rated for 4.0A/phase is over the 2.5A/phase maximum of the XS3525/8S-3. Running in series requires only 2.0A/phase to achieve the same torque. The disadvantage of this method is that it raises motor inductance, which in turn, slows motor coil charging time. Since proper torque is reached only when the coil has charged to the required level, the longer it takes to charge, the longer until full torque is achieved. This leads to slower full torque stepping rates. Conversely, a half-winding configuration requires full nameplate rated current, but if the drive is capable of this, the advantage is that rated torque can be achieved twice as fast as series winding (using the same voltage, when comparing half-winding and series).
Originally Posted by dertsap 
