Alliance are a serie of different mods. On the Star Wars GC, you can play the civil war Empire vs Rebel era + Black Sun and soon the Republic and CIS.
The 7.3bX is a special version thought for people with crashes to desktop when the battles ends.
If you want install the 7.3bX, you will need the 7.1b version + 7.3b patch. It can be a upgraded 7.0b or a 7.2b. Always with with a full installation. I would not trust at a mods folder installation.
Unfortunatelly the 7.3bX does not add any campaign, from FOC, EAW or the new campaign. The features from these campaigns do not work very well with the additions in the mod and the Gold, Steam or GOG game versions. Perhaps with time it can be made.
However, most of the special reinforces from units have been changed and now sometimes, you can find very big battles. Probably you will think how they will not be good and the game will crash. But the point is how the 7.3bX is a lot more stable.
It can be found only at Firefoxccmods.com