Unfortunately, this game just doesn't have enough people playing it online to really make mods viable. For some reason, 99.5% of all Sins buyers only play the game offline in single player against AI. It never attracted the online multiplayer PvP crowd. So, if you want to play real Sins games (no AIs) your only option is pretty much the mod-free Diplomacy game on the Diplomacy expansion. The game is awesome though, so it's worth playing as is.
It is possible to play mods, but those games will almost always be vs. AI and you need to hook up with a group of people who also want to play that mod and schedule it in advance.