Hi Ray,
I agree with what Doug has said although I have no experience with recording with the SM57. When you record with K&K directly plugged into your recording device you won't need a preamp. I recorded once a song with that technique and the resulting sound is very direct (
The water is wide), too direct. Acoustically you are much better of with more air in your recordings. The advantage of the 'direct technique' is that you can record in a noisy surrounding; though not too noisy because the K&K picks up a tiny bit of the surrounding noise via the sound bord (at least in my experience).
Karel