I have two GPS units (530 & 430) with HDMI in from RealSimGear, they are only fairly low resolution so it seems a waste to use a GPU output on each. I am running out of outputs and would need to buy a 2nd GPU soon.

Maybe there is a solution (software/hardware) that takes a high res image / screen and then only pipes certain dimensions of the high res image to separate HDMI outputs?
So the windows machine would just see a normal 1080p screen which you would drag GPS1 to the top of, and GPS2 to the bottom, then this solution would output the top half to HDMI1 output and the bottom half to HDMI2 output.

This would mean I could use multiple small/low res instruments from one high res GPU output, avoiding the need for a 2nd GPU.

In image below I describe what I am talking about. The blue is the GPU output (High res) and the red are the defined dimensions for the subsequent outputs, so I can use 4 low res instruments using only 1 precious GPU output. 

If no such product/solution exists, can you suggest other solutions? 
Do USB to HDMI boxes/dongles have their own GPU and are suitable for windows machines? How many of these would be able to sit on a USB hub?🤔

I run 7 displays off one computer with one graphics card.  Two of the displays are using USB to HDMI.  4 displays run off a 1070ti.  Another display runs off the integrated graphics card on the MB.  Everything works flawlessly.  This is for a 737MAX cockpit.  External visual displays run off a separate computer.