The MIT-129 is for impedance matching of a high impedance ¼" phone equipped source (like and electric guitar) into a low-impedance (mic-level) XLR type input.
To run a low-impedance XLR terminated line (like a pro microphone) into a high-impedance ¼" phone input (like a guitar-amp input), it's often necessary to use a line matching transformer like the MIT-435.
