There is only one headphone jack on the Digi 001 Interface. This setup can be used to create additional headphone mixes as needed. The Digi 001 Interface, has four stereo Output pairs. This will allow you to create four stereo headphone mixes. An external headphone amplifier will be needed to complete this setup. (Headphone amplifiers are available from Furman, ART, Fostex, Rane, and Behringer.)As an example, send the drums, bass, guitar and the vocals as one headphone mix. Bus the sends of these tracks to Monitor Outputs 3 & 4 of the Digi 001:1) Create a second Master Fader in Pro Tools LE. File Menu > New Track > Create a Stereo Master Fader > Press Create. Set the output of the Master Fader to Analog 3 & 4. This is the overall volume sent from Pro Tools to the headphone amplifier. 2) In the Sends View window in the Mix Window, set the sends on the drums, bass, guitar, and vocal tracks. (The Sends are the buttons with the diamonds on the channel strips in the Mix Window). a) Click on a send button for the drums and set to: Interface > Analog 3 & 4. Do this for the bass, guitar, and vocals as well. b) Display Menu > Sends View Shows > Select Send A. This will allow the send to have a send fader to adjust the volume level being sent to the headphone mix. 3) Connect balanced (TRS), quarter inch cables to Outputs 3 & 4, on the Digi 001 interface, to an external Headphone amplifier. Connect headphones to the headphone amplifier and adjust the Pro Tools Sends mixes to your liking.