For most games you don’t have to set the DK2 as primary monitor. If you haven’t done so already, please check the DK2 setup guide in the documentation. It explains how to setup vorpX with the DK2 as secondary monitor. Normally ~90% of games should work this way.
Dirt3: One thing you could try is switching from DX9 to DX11 or vice versa. Normally both should hook, but maybe one works better for you. (DX9 is preferred due to Geometry 3D support)
For Dirt 3 there is a Game Optimizer entry in the vorpX config app that allows you to switch to DX9 automatically.
in case the Game Optimizer fails for some reason, you can also do this manually:
1. Open [My Documents]\My Games\Dirt3\hardwaresettings\hardware_settings_config.xml with a text editor
2. Search for forcedx9=”false”
3. Change the line to forcedx9=”true”
4. Save the file