Four jumpers on the digital card can be made to disable channels 5-8 on the AES Output. This is so that a standard 25-pin to 25-pin Pro Tools cable can be used to record channels 1-4 at 192kHz. (Half of the connections on the Digidesign Digital Input are used for receiving and the other half for transmitting.)
For more information, consult the relevant section of the Pro Tools User Guide. As shown on the card, with the jumpers in the lower position (on the bottom two pins), outputs 5-8 are enabled.
Removing the jumpers and placing them in the upper position (on the top two pins) disables outputs 5-8, as shown: