bluntforcetrauma, a preamp basically just amplifies the signals from a pair of microphones. Ideally it has no sonic effect at all--neither on "dynamics," nor on "vertical displacement," "picking up a broader higher range," the brightness of the "musical capture" nor any other such thing.
A preamp that has any such effects should be regarded as broken in my opinion--or at least as a severe liability for live recording purposes. It's more like a preamp plus an effects box, where the effects box has a mind of its own and won't let you bypass the effect or turn it down--which is simply bad design.
If your microphones put out only 25 mV when the music is at its loudest, and your recorder works best with 750 mV coming in, you would use a preamp to raise the 25 mV to 750 mV for that reason. It's purely technical. If your microphones put out 10 mV and your recorder does just fine with 10 mV coming in, don't use a preamp. That's what it mainly comes down to.
A preamp (or preamp stage of a recorder) that has audible coloration is usually an unwise choice for live recording. When you think about it, there can never be an effect that's always an improvement no matter what the original signal was. If there ever was such a thing, then after making the live recording you'd want to run the recording through the thing again--and then again, and again and again; the sound would always keep getting better and better each time. If you find me a circuit like that, I'll change my opinion.
But until then, I'll insist that preamps for live recording should be audibly transparent, and any flavoring or coloring (be it EQ or compression or reverb or distortion or fancy tricks with stereo imaging) should be added separately--afterward, in the comfort of your home or studio--so that you can actually listen to the effect and adjust it to suit your tastes and purposes.
When you really listen, surprisingly often you will end up choosing to add exactly nothing. I'm amazed at how often I set out to improve a recording with signal processing and then after spending half an hour tinkering with various settings, I compare it to the original and end up choosing to leave it the hell alone, because it may not sound perfect, but the sound as actually recorded has a kind of truth to it that I prefer.
--best regards