I'm gonna go with a larger Supreme group. Same people, who will probably as a treasure trove because they once interacted with the various peoples' ancestors. They'll be powerful, but just split into three separate, semi independent fleets. All the nations can accelerate and grow far faster than the Supremes, so while in the beginning, Supremes may be more powerful, they'll be a bit left behind in terms of manpower later on. 

Obviously, there would be Supreme humans, Triarians, Abh, Dolphins, and other major races. Supreme Humans and regular Supremes will more than likely make up most of the current Supreme population, since humans are average at everything, and while they are a bit more morally and emotionally involved, it would probably be considered as cultural enrichment 

Is that all right, Keyguy? Darkwoof?