Motherboard won't produce a display output if you are using an installed graphics card.
Well that depends on the motherboard and if he/she has the igpu enabled in the bios in the first place. That said there is no reason he/she can't run the third monitor off of one of the GPU's in the first place. You really do not need to connect it to the motherboard. But it would help to know what hardware/OS you are running.
Motherboard won't produce a display output if you are using an installed graphics card.
Well that depends on the motherboard and if he/she has the igpu enabled in the bios in the first place. That said there is no reason he/she can't run the third monitor off of one of the GPU's in the first place. You really do not need to connect it to the motherboard. But it would help to know what hardware/OS you are running.