You can try to re-arrange the wood so the Discus can't hide so much. But have the Discus been in there as long as the other fish. Maybe they just need more time to get used to the tank and you. It would seem after awhile they would start to gather near the front like the others when they think they'll get food. But maybe there just shy right now. You do have a lot of different light types. I like the LED in a deep tank it gives off a nice shimmer effect. Maybe go with all 30W LED