Using mic pre that, in turn, goes through onboard pre of DAW...pointless?

[Reggaesoldier]

Just a little bit, probably not enough to really notice as long as the "trim" knobs on the mixer are turned all the way down. If you can bypass the mixer and run the preamp right into the soundcard; that would be your best option. But it all depends on what you're trying to do, you may need to run it through the mixer for a different application down the line.