You might want to try freeze dried cubes of blood worms because they absoutly love that or at least mine do. you also might want to try brine shrimp cubes.
D. Gouramis are brilliant, i've had mine for a month or so... I'd definetally get some frozen bloodworm, just defrost in a little tank water and pour it in.
I can't get mine to feed on anything other than bw!