Resolved 2 Video cards, but can only use one

A friend at work gave me his old computer; an Alienware X51 R3. Intel i7 3.4ghz 8Gb ram, Win 10 Home. It came in 2 pieces, the desktop and another big piece he said had the GPU in it. I connected it as best I could, he wasn't sure as someone set it up for him. He's a console player so wasn't all that sure about it. But anyway, I have a cable from the bottom part, containing the GPU to my monitor, also one connecting the GPU part and the tower together. Everything is working fine. I downloaded the latest Nvidia drivers and GeForce Experience software and it shows both cards; GTX 980Ti 2GB and GTX 970 4GB. Every game I run, only shows the 980Ti. Unless the 970 is in the tower and not the GPU part, I don't know why I can't select it anywhere.

 

I don't think I'm able to do this. I was able to see both cards. I found another connector on my tower. One HDMI is to the onboard intel video the other is for the 970 in the tower. So I have an HDMI to the 970 to my monitor and a DVI going to the Amplifier where the 980Ti is to my monitor. I can't SLI the cards because they aren't together so I can't bridge them.
So, I can see both cards now, but I guess I have to choose which card to use for each game...

 

I delved a little deeper and found that the 980Ti is actually a 6gb card! I looked at the advanced display settings in Windows 10 and it reported 6gb and also found another piece of software online that gives a ton of info on nothing but video cards and it also reported 6gb. So I disconnected the HDMI and am just sticking with the DVI to the amplifier. Thank you for your help!