Sad Spires comes in two flavors - 2 & 4 player versions. It also has a working tunnel system curtesy of fuggles for quick redeployment of your troops. Should work on Dark Crusade as well as Soulstorm.
A more greyish map with a simple layout. You can use the tunnels for advanced mobility. Readme says it should work on Dark Crusade, too. Just can't remember after such a long time but I guess I can trust my old self.