Your Planet system should be fine for the job, it lacks the complications other transmitters might cause.
You don't say what the problem is, but I'm guessing you're not getting sufficient swing on the schottels? You need to put a servo booster on each schottel (such as Action Electronics (from Component Shop) P96 Servomorph. That will give you 180 degrees lock to lock. I've got a couple of tugs using schottels (one has Graupner schottels and the other one from Oceanworks) each one gives a full 180 degrees on P96s).