Maybe a can put in my own opinion, since that's really all forums are is opinion. I would use your current sand mixed thoroughly with your new sand first. Here is the method I would use for what you are trying to do...
1. Take out all of your corals and livestock put it in a Rubbermaid bin with enough water to cover.
2. Remove your current rocks and sand. Mix your world sand with new live sand. The new live sand will be seeded as opposed to dry sand which is basically a wasteland desert for bacteria.
3. Get a big bucket or brute or Rubbermaid bin with fresh saltwater and shake, scrub and blow all the detritus from the old rock and the new rock.
4. If you use anything like focused or starboard under your sand put that in, then do a quick rock scape then add your sand. Add the remaining old tank water to your new setup and then continue to fill with saltwater that was already been mixed to the proper salinity..
5. After the tank water is at the proper lever to run begin running all filtration including skimmer and filter sock
6. While the water is warming up you can get your aquascape a bit more desirable and use this time to allow any dirt and debris to settle from the water column.
7. After things are a bit more clear start doing a drip acclimation to your livestock that is in the Rubbermaid bin. You can let this happen for several hours, replenishing water in the tank from water in the bin..
8. When you are happy with your acclimation period, quickly add 100% of your livestock.
Turn off all your lights and make sure your corals are a safe distance from each other and let everything settle in for the night. Tomorrow when everything is looking g better create your final aquascape, keeping in mind that any white, uncolonized rock exposed to light has a great probability of becoming an algae farm (most likely bryopsis). After your somewhat happy with you design you can start begin placing corals, but be warned that the lighting and flow is going to be different from your smaller tank and you might have to condition your corals to there new home over time by starting them off low and transitioning them higher over a period of up to several weeks.
Test test test and don't add anything new until you are satisfied your tank is cycled to your old inhabitants. Be patient and change your water at least 10% weekly or more as needed to control any possible ammonia levels and nitrates. Be careful, I call this a "hard" transfer method and sometimes it's necessary when you can't have 2tanks running for a month and a half until your new one is ready. It should work well so long as your both patient and vigilant.