If you have an NT1A, don't even bother using the SM57 on an amp like that. It isn't a stereo amp, so you just need to use one mic. Place the mic right at the center of the speaker and back about 2-3 inches. Make sure to give the amp a good ammount of volume so the mic gets a good loud signal, but not too loud as condensers can clip the signal alot sooner than a dynamic can. If you need more body, try placing another condenser behind the amp pointing into the open back of the cabinet. But remember that you'll have two mics pointing at each other, so they'll be out of phase. If your preamp has a phase reverse switch, kick that in. Otherwise you can do it in any sequencer, I think, as long as you're not recording into a single stereo track but rather two mono tracks. Buena suerte, amigo!