Ideally you should upgrade to a modern video card, the RX 580 is near 50% faster than the 6990 even assuming 100% multiple GPU scaling, not to mention 2GB VRAM is really too small for modern games with higher resolution textures, not to mention the HD 6000 series and earlier are legacy products. But if you're not interested in that, in GPUz does it state Crossfire Enabled or Disabled?