I would pretty much guarantee they will devour the FD earthworms, just cut them up into appropriate size ( i use scissors) and rehydrate the pieces for a few minutes...and watch em go to town! If yours eat just about anything i probably have plenty of things that would be good for them. I have a soft spot for discus, i have never owned any, but they have always been very high on my list of fish to keep! So i get excited when some one is trying to pick out food for them.
The plankton gold is 48% protein, 9% fat, not sure on carbs but there is nothing listed as far as a filler or binder like corn meal or wheat meal or anything like that. Fish protein, egg, zoo plankton, and milk protein (plus yeast and soy) are the first ingredients listed. And as you noted it has naturose (and spirulina) included. The quality of these flakes seems much higher to me than most of the other stuff i have tried, but i guess i cant verify that for sure. I have sent out quite a few samples of it, but i havent gotten any direct feedback on it yet either.
So anyway, let me know if you decide to try some of this stuff out!