Okay, I should have asked what the OP wants/needs out of the setup? The Mbox digital out is SPDIF while the Dbox digital input is AES, so that connection requires some kind of converter(I'm no digital expert so I can't comment on that). If the OP wants to make the most of analog summing, then Mbox is probably not the best choice of interface. Maybe something like a 003R with 8 outputs(plus main outs) would take better advantage of the summing abilities. I was steering towards the most basic so the OP could hear audio
