Any advantage having a 3V Dac output?

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.

I believe that 15 dB gain (which is low -- most amps have 20+ dB of gain) means that the amp needs about 2 1/2 volts input for full power output. He should be fine with the 3 volt output of his DAC.