@reload2024 8K is going to be expensive, the controllers dont seem to have drifted down to the cheap gear yet.
Maybe 2x 4K to 1 to 4 video wall controllers will do: https://www.aliexpress.com/ite...
These are so cheap you can buy spares - there sure wont be a warranty service.
The good news is that you can now get a good video card - the NVS 810 does have a lot of outputs but only 4gb memory and it is very old tech.