Give Slice Master 6000 a try and let it configure every thing for you. HRD Support is pretty good at this point.
To get DM780 going, just download Slice Master and start it up. Then, in SSDR choose a slice set it for DIGU and select a DAX audio channel. Make sure the DAX channel is enabled in the DAX Control Panel.
Then back in Slice Master, select the Launch tab for the slice you chose in SSDR. Scroll down to find the DM780 option group and change the Launch setting to "By Mode". Now any time you switch that slice to DIGU, DM780 will pop-up ready to go.
If that doesnt work, Slice Master will display a status messages telling you what you missed.