PS: Also attempted whether installing the latest AMD gpu-pro 17.30 kernel driver for my AMD Radeon 4 GB R9 380X Nitro would change anything; i.e. under Ubuntu 16.04 LTS.

=> Yet apart from the console command:
lspci -nnk | grep -i vga -A3 | grep 'in use'^C

now putting out:
"Kernel driver in use: amdgpu"

=> nothing DOS2-wise changed so far.

(IF YOU TRY ANYTHING ALIKE: BEWARE OF COMPATIBILITY-ISSUES AND THAT ONE MAY THOROUGHLY SCREW UP ONE's VIDEO OUTPUT - HAVING TO SPEND SOME HOURS WITH LIVE-CDs AND CONSOLE COMMANDS - IF THINGS GO WRONG!)