However the developer really needs to start living up to their patches. They said that SLI / Crossfire support was added in the 1.5.x release but guess what? that 2nd card is still idle. nope, a lie. for a source engine game, this is kind of unacceptable.
the only way to get SLI is a custom profile download via GFE. Or use some of the download links in the forum.