Original Sins of a solar empire dvd version

Heya all

So, a while ago i bought a "Games for windows" dvd version of the original SoaSE.

More recently i've installed and played it, though steam won't accept the cd key to register and be able to download patches and the addons. I've managed to register the game with the correct Stardock main website, then was able to download an installer for the most recent 1.195 game version, but when i try and get entrenchment or diplomacy it says they are sold out...

Does anyone know a legit way to obtain these addons to the base game? I've looked all over and the only way i can figure is to re-buy the game on Steam, which realistically i'd rather not do since it'll cost me way more than i'd planned!

Please, can anyone help?

Cheers!