Alan, you're going to become frustrated with your options
I've been struggling with the same question for 8 months. You have a ton of options, but the place to start with is telling us what kind of corals and livestock you wish to keep. Basically, we need to understand if you need low, medium or high intensity lighting. From there, there a dozens of options based on the dimensions and depth of your tank. All the different lighting options have different pros and cons, such as electricity use, heat generation, light output, spectrum, price so it is critical you let us know what you are going to want to keep, SPS hard corals, softies, LPS, Clams, etc.
You can use any lighting that fits over the tank, and if you are already hosting corals with your current lighting setup, then you should be ok on the 55. Since you are going larger to smaller, that will work out positivity for you.
Fish only tanks just need lights, the fish would be fine with any type of inexpensive lighting. Light the tank to your taste. I like the look of the doublebright LED lights for a fish only tank.