Hi. At a push you could connect the main mix output of the first desk to either the aux in, tape in or even to 2 channels of the second desk in a sort of submixer scenario. Similar to the analogue world where you would connect the mix bus output of one desk to the mix bus input of another. For the purposs of effects and sends, though, you'd be operating 2 separate desks and you'd basically just be mixing the outputs together.