A 57 is not the ideal mic for any of these instruments, but it will give you a clear, pretty accurate picture in each case if you do a good job with placement. It will probably do the best job on the bass, and that's the main point of the recording. A small diaphragm condenser will would probably do a better job on the guitar and piano.

All of the music schools that my daughter applied to SAID that they didn't really care about professionally recorded audition tapes as long as they got a clear impression of your ability to play the instrument. She was adamant about not adding reverb or eq. (I added some eq anyway. Heck, a mic affects eq.) I expect that if you do a good job with the equipment you have it will be fine.

Take some thin foam, washcloth, carpet scrap, what ever, wrap the microphone in it. Then very carefully, stick it in the large hole of the bridge. You'll have no problem with low end recording. The 57 is just fine for everything. Of course, if it's jazz and you're not Rudy Van Gelder, you might need more than a single 57. I mean, do the math. 2 inputs, 3 instruments. OK, so put the guitarist in front of the piano. Then you only need two. So why did you get an M-Box 2 with only a single microphone? What were you thinking? You could record stereo by just doing everything twice? Recording a time with the microphone first plugged into the left Channel and then recording it again plugged into the right Channel? Time delay multiplexing? That's not what it means. I think you are obviously a professional otherwise you wouldn't have ProTools? I have been doing this stuff for over 37 years but I only became a professional 3 years ago when I purchased the same thing. I don't use it because I don't like it but I have it and it's only because people kept on calling me asking if I have ProTools. Now I have it and they've stopped calling?

Please leave a message at the sound of the 440 hertz tone.
Mx. Remy Ann David