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From what you're suggesting it sounds like I may want to carry all the control signals on the same ribbon cable, have the ribbon cable connector somewhere in the middle of all the analog switches, and then have the ground between the two boards pass along this same ribbon cable? In this case the other ground between the two power supply sections would be eliminated, and since there's a ground plane on the analog board anyway it shouldn't be a big deal to the analog circuit exactly where the ground comes in?