the unit has 2 DSPs. It's very important you decide how you want to route them in your stereo setup:
you then use 2 inputs and 2 outputs to connect to the rig.
Anything loaded in A will also be processed by B.
you can use 2 inputs and 2 outputs and configure routing internally, in the H8000.
or you can use 4 I/Os, assigning 2 to DSP A and the other 2 to DSP B. This is a more versatile setup but requires an external mixer/router to properly manage 4 channels in a stereo setup.