Power to the mics is good--it makes them less likely to overload.
Too much amplification from the preamp is not so good, because it can overload/brickwall the recording.
You probably want to go mic-->preamp-->Line-in instead of Mic-in, since Mic-in leads to the recorder's own preamp. With Line-in, you're bypassing the built-in preamp with the better, external preamp.
And you probably don't need to add too much amplification from the preamp if the concert is loud. Do some experimenting with your stereo on appropriate levels, and then lower them further when you get to the blast of a live show.
I was afraid I would over power the microphones if I used the preamp
Best wishes
Steen