i dont know that a JD would work, necesarily they like to be on the bottom for the most part, digging through rocks and what not, you wont have a happy dempsey that cant have a cave and is forced to swim upwards.....plus they like to feel like it is their tank if its a 55.... it always depends on the fish tho......
i would say start with what you definately want to put in the tank (what you want to be the main attraction).....
then go from there, try to get some information from snakehead owners too, look at what they got in theirs, cichlids may not be the best route in this case, but just be patient get your killer and go from their