Depending on what exactly you are trying to achieve during recording and mix down your options can vary. Option 1 - you can put (2) SX 1's together. Option 2 - You can pickup a MX-2424 and sidecar it to via the built in adat port and adat expansion cards. There are a few threads on here and the old board detailing the creative routing for both options. Depending what you actually require. Good luck.