Enjoy this great guide how to enable CrossFire support for Virtual-O made by Angus Haines. Thanks!
I have just provided recipe how to run Virtual-O in exclusive mode and Angus have researched it further and tested. I’m pretty sure hat you can perform similar steps to enable SLI for NVIIDA cards.
CrossFire setup guide
To enable Virtual-O to utilize AMD CrossFire you first must force the game to run fullscreen (not windowed borderless, the default setting).
To do this you need to go to your Steam library, right click on Virtual-O, Properties and under General click ‘Set Launch Options…’ and enter the command line:
Then open AMD Radeon Settings, Gaming then Virtual-O (if it’s not there, then click add in the top right corner and either scan or add it manually).
In AMD CrossFire Mode I found that using ‘Optimize 1×1’ resulted in the best performance.
Once you have launched Virtual-O make sure to have Antialiasing set to FXAA or lower, as TSAA results in some serious issues with outlines, and to have V-Sync enabled to reduce screen tearing.