Manual says that it is a Total RMS 25 W rating ... and that it plugs into a 3.5 mm stereo headphone socket. Since it has its own power supply cord for 120V/60Hz, that implies it has its own internal "signal" amplifier.
The above page indicates that the unit has its own "power and volume control pod", so presumably the setting on the computer side can be at max, but I would make sure the setting on the "pod" is set to lowest value before cranking up the computer's output setting.
To be on the safe side and avoid "clipping" which would destroy speakers, I recommend
if using the headphone setting, keeping your default set to 50%, or
if using the line out setting, using the 100% setting.