Gigabyte's technical support
This is the same config as the Aero 15 x8 I am running.
It is possible to turn off the Laptop display, and only use the HDMI and DisplayPort displays. I have seen that this drops the usage of the Intel card to near zero.. but its not off. Running Isadora in this configuration needs more testing but it seems to work well.
Generally, Isadora works rather well with the laptop screen active. There is a known issue with preview windows sometimes pushing the LOAD above 100%, but this doesn't seem to occur when stages are full screen (out via the dedicated card).
I have not been using the Thunderbolt output.