Apollo, you can play any version of Sins you want--the original Sins, Entrenchment, or Diplomacy. "Trinity" is merely the name of the package that includes all of those games. Find your main Sins folder in your Program Files folder and you should see three separate .exe files for "Sins of a Solar Empire.exe", "Sins of a Solar Empire Entrenchment.exe" and "Sins of a Solar Empire Diplomacy.exe". Make shortcuts to them out on your desktop (or wherever you like to put them) and you are ready to go.
Note that if you try to join a game and receive a "Your Mesh Files Differ from the Host" error, you have to go to this thread to learn how to fix it:
https://forums.sinsofasolarempire.com/341480