Use the -forcehighpoly command line argument.
Full details of this modification are here.
Soulstorm was a very incomplete expansion, and due to the demise of Iron Lore Entertainment shortly after its release, there was little to no post-launch support.
An extremely dedicated group of individuals put together this "alternative" version of Dawn of War. While an acquired taste and significantly different to the base game, it offers a more intricate and interesting experience, with unit roles switched up, some upgrades that were removed in expansions restored, and additional content created by the community. All units are designed to play a role until late game.
The mod can be downloaded here.
The mechanics in the Campaign changed between Dark Crusade and Soulstorm, causing the loss of "consistent bases" (buildings built in previous missions are there for the next mission on that map). This can be fixed by installing this mod.
It is possible to run multiple modifications at once. For instructions, see here.
Dawn of War\Engine\Data\