There is a difference between one preview window over all screens and 16 fullscreen windows: MadMapper will ask the GPU to render surfaces for all contexts, change context more times, switch from one texture to another more times per frame etc.
There is an hidden setting to create a single display over all the screens. We should make it public in the future. If you activate this setting, you can create only one projector, choose the top left screen and set the projector size to the bounding rectangle of you 16 screens in Windows (ie 4x1280 x 4x720 = 5120x2880).
To activate this setting
on macOS in Terminal.app: defaults write com.garagecube.MadMapper adjustProjectorWindowToScreen 1
on Windows, in cmd.exe: REG ADD HKCU\SOFTWARE\Garagecube\MadMapper /f /v adjustProjectorWindowToScreen /t REG_SZ /d 0
Does it solve ?
Btw, the NVS 810 card is great to have 8 outputs but the benchmarks show poor results. Let us know how it works in your configuration.
Matthieu - MM team