There are several good total conversions for Sins of a Solar Empire: Rebellion. Star Trek Armada 3 is the most complete overhaul I’ve played for it. I’m a big fan of Halo spaceships and the Sins of the Prophets mod is the closest thing I’ve seen capture the asynchronous battle between UNSC and Covenant ships. There are others for Star Wars and Stargate that I hear are good, but I have not tried them.