The Orbit arrived today. I setup my tank with substrate and water tonight. You are right, the Orbit is not wide enough to cover the whole top. You could probably fit two on the top. I put the legs on mine at first, but then decided just to lay it on the glass top. It actually came with little 1/4 inch rubber feet that fit perfectly on the lip of the tank. Right now it is hard to judge because I have one daylight and one actinic bulb. I ordered the wrong size daylight to replace the actinic, but I have ordered the right size. When the correct bulb comes in I will put it on and see how much light I get. So far it looks really good. Also it came with two lunar lights, not the one lunar light the descriptions state. Construction looks good. The fan is noticable but I wouldn't consider it annoying. It may take a little getting used to depending on how sensitive you are to that sort of thing. The tank is in my living room close to where I sit to watch TV. I can hear the fan in the background of the TV noise. I asked my wife and she said that she wasn't annoyed.
I saw a Coralife Quad at a local pet shop. It is smaller than I thought it would be. It actually has a really slim profile compared to the arched Orbit. I think it was similar in width to the Orbit. I'm glad I picked the Orbit over the Coralife Quad light. So I would really suggest the Orbit or AH supply depending on how much work you want to put into it. It did feel good to slide the Orbit out of the box, take off the protecting styrofoam, plug the bulbs in, plug the cords in, then flip the switch and Viola light!
Good luck with your decision. Please post what you finally decide. Maybe we can share cube experiences.