The answer to your question is system dependent -- what’s the input sensitivity of your power amp? If it only takes 1 or 1.5 volts for your amp to output its full power, then your 3 volt DAC output is largely wasted -- you’ll need to either turn down your analog volume control a lot or reduce the volume of the digital signal being fed to the DAC.
Keep in mind that once your amp is outputting its full power, anything beyond that is just clipping. Putting extra voltage into the amp’s inputs doesn’t increase the available max output. And, if your amp uses a traditional potentiometer to control volume, these pots often track most poorly at the lower levels (9 o’clock and under), meaning you could end up with more channel imbalance that you would have if the volume control is turned higher to achieve the desired volume.
OTOH, if you have a power amp with a low sensitivity input, the 3 volt output will help you without needing additional gain from a preamp.
