El Capitan Rejects Two Graphics Cards? (Mac Pro 2009)

Hello,

I recently upgraded from Yosemite to El Capitan. When I first tried to install the OS, I received a Kernel panic (gray screen "system restarted for unknown reason").

After looking on the forums, I found it to be an issue dealing with anything non-Apple product, so I removed all peripherals, nothing, removed my second graphics card (nVidia GTX 770ti), ran with my nVidia GT120 (Apple original) and the OS installed without any problems. Thinking it was all over, I put my second graphics card back in, but whenever I tried to turn my computer back on, I received the same kernel panic. I tried taking out my 120, and only running the 770ti, but the computer did not start properly (blank screen, assumed kernel panic).

So right now I am not using my 770, until things become better. I have nVidia drivers installed for my computer, update 346.03.02f02 . The reason I bought this Pro, was for the expand ability options with updating the graphics card for programming and playing video games.

I am not upset about this, as the OS came out less than a week ago, so there are bugs bound to happen. But my question is, anyone else having issues with two graphics cards? Or have any suggestions that may improve my situation?

Thank you! 🙂