Hey Jessa, great question. It also depends on if you want to use the outputs on your Digimax DP88s as well, or if you just want to use the Digimax DP88s for additional inputs.
If you just want to use the DP88s for additional inputs, then you just need to use ADAT cables to connect the ADAT outputs of the DP88s into the ADAT inputs of the Studio 192. So that's ADAT Output (1-8) on your first DP88 into ADAT Input (11-18) on your Studio 192, then ADAT Output (again, 1-8) on your second DP88 into ADAT Input (19-26) on your Studio 192.
If you also want to use the outputs on the DP88s, then you need to connect the two ADAT outputs of the Studio 192 into an ADAT input on each DP88, respectively.