IMO and many on this board - DSB is a great way to go.
Also IMO - If you can remove half of your live rock and put into a large plastic container tub, remove some of the water to that container, add a heater to maintain temperature .... Then remove everthing else from the tank and put it in your tub including all inverts and fish ... Then lastly add the balance of the water from your tank ... you'd have an empty tank then. Ideally have both aquaclear 150's running on the tub while you swap substrates. If they won't hang on the side of the tub, at least remove the biomedia and place it in the tub as well.
You may want to rinse the biomedia in a small amount of your old saltwater ( removed from the tub in a small bucket ) if it is heavily fouled with trapped wastes first. Add powerhead to tub and you're ready for sand change.
Scoop out the old mixed CC/sand substrate. Some folks are placing some of this old substrate in a ladies stocking/pantie hose, to help seed the new sandbed. Others just toss it out.
How you intend to do your sandbed is entirely up to you. Some folks put down base rock or live rock base first - then add sand. Others lay down desired depth of sand ... then add rock.
It's up to you - personally I like having the DSB throughout the tank - then add rock "on top" of sand, pressing the first layer of rock down into the sand a little as I go. It's up to you.
You'll hear the pro's and con's of doing it either way.
Once you have some of the rock in place, begin to slowly add some of your saltwater from the tub back to your tank. Continue doing this, building your rock structure ... and eventually you'll come to a point when you must start adding the inverts and fish back. Check temperature of tank first, and if good, then add your critters.
Once all is back into your tank - add your 2 aquaclear 150's, powerhead. Allow tank water to settle - it may be cloudy.
Note: Ideally if you are planning to add live sand in the future - adding it to your new sandbed now would help to reduce any recyle. Although if you work quickly, and keep everything wet and warm during the process, I don't think you'll have much of a recyle at all.
If so ... very minimum at best.
Now would also be the time to decide if you are planning to keep both damsels, or not.
If not - great chance to remove them for return to lfs. If not - add the little buggers back then
My opinion - not 100% guarantee.
Good luck my friend
