Running one monitor per GPU on a GTX 690

Hello everyone!

I put together a new desktop using Zorin 16.1 Pro, with an GTX 690 graphics card. Ancient technology, I know. SLI is dead forever. Trying to make the best of it.

I'm having issues using each GPU to run a different monitor. I've been using the propriety Nvidia drivers that Zorin installs, trying to tweak things in X Server. I can get GPU0 to run two and GPU1 to run two, but if I plug one monitor into each, the monitor on GPU1 is black, maybe with a cursor if I'm lucky.

It's really odd, and I have no idea where to start. Randomly tweaking settings hasn't gotten me far.

I think a minimum of GT710 might be the issue, I could be wrong. I remember when I had my trusty GT620 it could not cope with Ubuntu based OS's based on Ubuntu 18.04 - That's when I jumped to GT1030. I decided to install a separate GT1030 for VM's but it didn't work - and the only OS that I could get to pickup both graphics cards (Primary VGA, secondary HDMI) was FerenOS!