Try changing the bulb to the XM (actually XDE, I guess) 10k and see if that helps. That's the cheapest and easiest thing to try first. Don't worry about actinic supplementation; that's mostly for color correction anyway. The 10k bulb will produce way more PAR (or PPFD, whatever you want to use as light intensity useful to photosynthesis) and that's what your corals need for health.

I still bet there's a water quality issue, though. Unless your new sand bed is heavily stocked with worms and other detrivores, probably it's not really functioning as a deep sand bed. When you put sensitive corals in this situation, subtle degrading of the water quality over time due to the new sand bed not being able to "keep up" with the bio-activity in a stocked tank can take place. I'm pretty sure that's what happened to my old tank after I moved it and replaced a lot of the sand bed, and eventually most of my corals died. It wasn't until I bought 100 bristleworms and all sorts of microverts from inland that the system turned around. In the old location, with a mature live sand bed that developed along with the corals in the tank, everything was healthy.

That's my theory, anyway. I have no proof for it, but it was really the best explanation.