I believe the only option for your machine is iListen. I have done a little research on this issue and, to my knowledge, iListen will only transcribe (convert to text) voice recordings if it is YOUR voice, and you have gone through the requisite training phase so that it adequately understands you. I wanted this for transcribing interviews (me asking questions, others answering) and found there
are no voice recognition programs - Mac or otherwise - that can accomodate more than one user.