Installing an additional GPU

[Si2006]

Problem Solved

sudo vi /etc/default/grub

Add "nogpumanager" in the following line
e.g. if you have this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

it should look like this:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nogpumanager"

Esc :wq to write changes and quit.

sudo update-grub

Reboot

Make sure that the following command returns true:
grep nogpumanager /proc/cmdline && echo true || echo false

If it returns true, regenerate the xorg.conf
sudo aticonfig --adapter=all --initial

=======================
export DISPLAY=:0
sudo aticonfig --adapter=all --odgc

Adapter 0 - Supported device 67B1
Core (MHz) Memory (MHz)
Current Clocks : 300 150
Current Peak : 947 1250
Configurable Peak Range : [300-1500] [150-2000]
GPU load : 0%

Adapter 1 - Supported device 67B1
Core (MHz) Memory (MHz)
Current Clocks : 300 150
Current Peak : 947 1250
Configurable Peak Range : [300-1500] [150-2000]
GPU load : 0%

Thank goodness for that!