Mixing different model/brand videocards only works with Hydra, not with Lucid Virtu for Z68/Z77 boards.
Virtu offers 2 modes, one where you use your discrete videocard as primary output while the cpu's igp is only used for the Quicksync video encoding feature. This works fine but at the moment as far as I know only paid software like Media Espresso can use it. Free software like Handbrake doesn't support Quicksync and works purely on cpu power.
The second mode is where you use the cpu's igp as primary output while the vidcard only kicks in when playing games. Technically this mode works as well, but the problem is it doesn't save any power since the vidcard isn't disabled at all when not in use. On the contrary, the vidcard won't even clock down during 2D loads since this is controlled by the driver which is bypassed in this mode. Therefore idle power will actually increase by quite a bit. So this mode is essentially useless.
Virtu also offers the Hyperperformance thingy where the vidcard and igp work together. I haven't tested this but I read reviews saying it doesn't work well at all, actually decreasing minimum framerates.