I don't know if you have done the workaround for the graphics card yet. I also have that card and a Z68 board and ran into some problems. First, connect your monitor to your machine through the onboard HDMI, not any port on your card. When you boot up, go into your BIOS (delete key on startup) and then find where it talks about display to initialize first (cant remember which menu its in - maybe peripherals?) and choose HDMI. You can now change your monitor to HDMI and unplug the DVI cable from your 6870. If you switch the monitor before completing the previous step you will probably not see the spot where you have to press delete because the motherboard won't have turned the HDMI port on yet since it should be defaulting to your card as the primary.
I'm assuming you are now booting from your Unibeast USB drive and are at the screen selecting your OS. Type GraphicsEnabler=no (it should stop the booting process as soon as you start typing.) This step should keep the bootloader from activating the 6870, if you don't do this you will see the apple and the spinning progress circle then it will freeze like that because it tries switching to the 6870 which will just display a white screen while the HDMI connection will be frozen with the apple on it.
Run through the install as normal and once installed, you can use the 6870 for the language setup and all that business. I don't know if I mistyped the GraphicsEnabler bit but when I restarted after the install completed, my 6870 activated and I had to plug the DVI back in and switch to it to see the screen. I knew thats what happened because my HDMI connection was showing the fabric like gray background as through it were a second display. Smooth sailing from there on out. I also suggest changing your BIOS back to initializing pcie x16 first as your display.
If the GraphicsEnabler=no doesn't work then you will probably have to disconnect the card entirely. I was going to unplug it from the power but leave it installed until I thought of the boot flag. I'm not sure if taking the power away is enough or if the card has to come out entirely.
Good luck!
