Some of the older versions of the firmware for the WFM700 series were written before the DG option was available and therefore are not able to recognize the card. If you are running an older version of firmware (v1.x.x or v2.x.x) then you will need to upgrade to the latest version of firmware (v3.0.6) before the instrument will recognize the audio option. The firmware upgrade is available as a free download from the Tektronix website.