The g68 user guide has a good diagram on page 14. User Guide

Assuming that you only have 3 DSPs and that you want to use the centre as master, the Slead(COMMs part) to the front mains(LR) needs to be connected to the centre output somehow but the Slead(Digital part) to the LR needs to be connected to the g68. If the centre and G68 are close you could connect the S lead to these directly, otherwise you employ the patch near the g68 and use another S lead to link from patch to centre as shown in the diagram.

If you have more DSP's, then you really need to use the patch. It is best placed somewhere near the processor as each additional pair of DSPs will have to connect to the g68 processor and the patch. smile

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REL Sub
Thinking about 218