Use the Intel and Nvidia GPU at the same time

[Floris]

Previously I used two NVidia GPU's to make a multiseat setup and  
everything worked as expected. Recently the computer had a problem and I  
switched the CPU. The new one have the Intel HD Graphics 630 display  
controller, so I was wondering if I could use the Intel and the NVidia  
GPU's to make a multiseat.

Unfortunately I have no luck to get two accelerated seats. As the NVidia  
GLX extension is loaded, the Intel seat is complaining: Failed to  
initialize GLX extension (Compatible NVIDIA X driver not found). Or I load  
the Mesa GLX variant and the NVidia seat falls back in the software mode.

Is it possible to load both the NVidia GLX and the Intel/Mesa GLX  
extension, or should I plug the other NVidia GPU back in?

Floris