All mics need preamps. Preamps just bring mic level up to line level, but they all have their own unique character (just like mics).
I've noticed a lot of Shure mics tend to be fairly low output. Before I broke my 57, I always had to crank the preamp to get it about the same level as the others. When you are looking at preamps, just look at the specs to see how much gain you'll be able to get from it. Well, look at reviews, too, I'm just saying that if you're concerned about the signal level from the mic, look at the amount of gain you'll get. M-Audio's Fast Track interfaces are not likely to be enough; I sold both that mic (the 7b) and a Fast Track to a guy once and he was freaking out because it came out so quiet.
If you're recording digitally, which most of us are these days, the level isn't that much of a problem. Making it louder in your DAW doesn't really add any additional noise.
thanks for your input, however, of course a mic needs to be amplified but there are preamps built into the presonus firestudio.
i was asking him about getting an external preamp since he had mentioned that the preamp that came with the presonus might not do the sm7b justice.
and there is more to a preamp than just gain levels.