Mal,
I haven't had a chance to work with this particular species, but I suspect the larvae which are much smaller and less developed than Banggai cardinal young, will need something at least as small as rotifers as a first food. I would take one of those spare tanks you have, wrap some black plastic around it, fill it with clean water and set up an air-driven foam filter with slow to moderate air flow. If you have access to live phytoplankton (greenwater), add enough so that you can't see accross the tank. I wouldn't add the phytoplankton until the larvae hatch. When you get larvae in the tank, add enough rotifers to get a density of 5-15/ml. For this first batch, just try to siphon as many as you can out of the tank when they hatch, but once you figure out how long it takes to hatch (I would guess less than a week, and probably more like 4 days - just a guess), you might want to try removing the father on the scheduled hatch date next time. If he doesn't spit the eggs out, you can place him in the rearing tank so that all the eggs hatch in there. If he does spit them out you can take the eggs and place them in an inverted soda bottle with the bottom cut off and a gentle stream of air bubbles to keep them suspended until they hatch. Then carefully transfer them to the rearing tank.
If you don't have rotifers and phytoplankton already, get working on getting some cultures going. I'm sure your cardinals will give you plenty more chances to try. Be careful though - aquaculture can become addictive.
Good luck,