Connect ADAT out 1-4 of DP88 to ADAT IN on 1824 with an ADAT cable.
Connect Clock Out of 1824 to DP88 Clock In with a BNC to BNC 75 ohm coaxial cable.
Set external sync on DP88 to Blue BNC.
With sample rates set at 44.1 or 48, you'll get a total of 16 channels; 12 with rates of 88 and 96.
Go to song setup to make full use of the available inputs and outputs to suit your needs.
It's best to save these settings as a default template.
Hope this helps.