One JD in a 55g would be the max for that tank, some would say a 75g. Either way, I tried a single JD in a 55g and think there are much better suited fish for a single species tank. I think a JD tends to do better in a community in a large tank. In a smaller tank by itself, in my experience and from reading on here other people had the same luck, the JD tends to be skittish and hide a lot. I found the JD a lot less personable than a Oscar, Chocolate cichlid, or Green Terror. All of which should be in a 75-90g minimum for a single specimen. I wish I could recommend a better fish to be in there singly with great personality like a Oscar, but the 55g does limit a lot. I would look into a 90g. You only add 6" of depth to the tank footprint. Consider maybe side mounting the filter if the depth is an issue.
For a community tank, 55g, I would recommend staying with the angels and adding plants. Or a community of Firemouths which can be amusing to watch.