Use display ports on mainboard and display ports on graphics card

I have a computer with Ubuntu 17.04, a Gigabyte Z87X-UD3H-CF mainboard and an NVIDIA GeForce GTX 650 Ti Boost.

At the moment, my screens are connected to the Nvidia graphics card - one screen using HDMI, one using DVI, and one VGA screen with a DVI adapter. I'd like to connect a fourth screen, but the only free port is a DisplayPort. None of my screens have a DisplayPort.

I tried connecting the new screen to the HDMI port of my mainboard, but it wasn't detected. It works just fine when I unplug one of the other monitors and plug it into the HDMI port on the graphics card. I tried connecting other screens (DVI, VGA) to the mainboard and none worked, so I guess Ubuntu disables the mainboard ports when it recognizes a graphics card?

Is there a way to use both the ports on the GPU and the ones on the mainboard so I can use my fourth screen? I am currently using the NVIDIA 375.66 driver.

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