I'm not real familiar with refugium filters, but you don't want to go too deep on your sand substrate. 2-3 inches should be more than enough for most cichlids.
Deep sand beds are a popular form of filtering for saltwater, if setup properly they create excellent anaerobic layers which will sustain nitrate eating bacteria. There are negative features though, I personally prefer plenums or bare bottom.
Refugiums are typically either a hang on back tank, sump, or even a second aquarium/rubbermaid tub filled with sand, beneficial macroalgae, and live rock rubble on either 24/7 lights or a reverse timer. Between the macro algae, scavengers (snails, crabs, star fish, etc.), pods, and such they'll really improve an aquariums water quality, stabilize ph swings, and even provide food for the main tank.