Any advantage having a 3V Dac output?

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. 

Even with a passive pre 3V may not be needed,  it depends on the input sensitivity of the amplifier. With an active pre, 3V can often be too much. 

Thank you all for your responses! My power amp is First watt F5 unfortunately the manual does not include the info regarding the input sensitivity!

@tiofelon diyaudio.com/passlabs is a good source for finding out more esoteric details regarding first watt offerings. In the below thread, they state:. "The F5 has a gain of 6times.The clipping voltage of the F5 is ~ 21Vpk, or 14.7Vac."

https://www.diyaudio.com/forums/pass-labs/218770-diy-f5-questions.html

That 6x gain translates into 15db, which is lower than many other amps but pretty standard for the first watt approach.  I don't know enough about voltage input sensitivity to know for sure, but I suspect that value is also lower than many other amps too.