Each DSP has 8 inputs and 8 outputs. Do not confuse the physical inputs/outputs with the DSP inputs/outputs, they are not necessarily the same. Depending on how much computation power an algorithm demands, it’s possible to load more or less algorithms within an DSP. An 8 channel operation would be, for instance:
Analog Inputs / Outputs 1, 2, 3, 4
ADAT Inputs / Outputs 5, 6, 7, 8