A DI box is a device typically used in recording studios to connect a high-impedance, line level, unbalanced output signal to a low-impedance, microphone level, balanced input, usually via XLR connector. DI boxes are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input. As the AudioBox USB 96 has both XLR and 1/4" inputs, you shouldn't need a Direct Injection Box.