Scott:
Can i ask does this fish eat dead foods now?
if not then you'll have to get it used to your tank(say feed it live food for a week or so-use ghost shrimp first(best of FW evils). Once the fish is happy in your tank, starve it for 3-5 days and daily introduce dead food which look alive- like silverside or mysis shrimp. You might have to do the fish on a string or fish on a stick routine, but get the lion excited and chasing it.
So to answer your Q? No cubes will not be enuf and they shouldn't be used as a sole food. Remember these fish in the wild eat shrimp, crabs, and fish. So you can feed them gorcery store bought shrimp chunks(w/ shells), crab meat, silversides, mysis shrimp, white fish meat, squid, octopus. I buy a bunch cut it into small chunks, and freeze it.
Rotate foods frequently, this provides proper nutrition and prevents food burnout.
As far as how much and how often. Feed the lion a few chunks each feeding and feed it 3 times a week.
Does this answer your Q?
frank