is it possible to use the voyager as a mic preamp without influencing the soung of the mic?
Well, the filter maxes out at 12kHz, so you may lose some sibilants. The main point of the Voyager’s external in is to process sounds, mostly through the filter. So your idea of a clean mic pre might not work too well.
You need a 60dB amplifier with a mic. There is no such thing in the Voyager.
The Voyager is designed to process/distort a signal.
If you want a preamp system that doesn’t color the sound, the Voyager is the wrong tool for the job.