Despite the QuPac having the Qu32 brains, which includes 2x st mtxs, it only has the physical IO of a Qu16, and the physical outputs on the QuPac are already assigned to mix outs and LR, which is why at first glance it seems you can only get mtx outs if you use an AR.
What I imagine you could do is set up a mtx, dial in the delay, then set either the AES socket or alt out socket to source its signal from the matrix. That way you can get a mtx out using local outputs without an AR (or you could get creative with the pafl bus.) As Mervaka said, the delay you dial in would be part of the mtx processing, not specific to the actual socket. This works on a QuPac because the QuPac has Qu32 brains (which include 2x st mtxs.) It won’t work on a Qu16 because the Qu16 doesn’t have the mtxs to begin with.