I just want let you know that if you have problems like the system restarts when you select "shutdown" to power off or it firstly powers off and then powers on again just after a few seconds in infinite loops, i managed to get rid of this by doing so:
- disabling ErP in BIOS
- disabling USB DAC Power
This disables the system consume least power in S5 (shutdown) state. When you stop here you already have fixed the mentioned problem (Gigabyte MLB). In this state you could still power on your system with keyboard, a mouse movement or click when connected to USB DAC ports. To get rid of this just diable USB DAC Power in BIOS. You'll loose this ports. However you should have enough USB 3 and 3.1 using without DAC Power.
I tested lots of shutdowns via menu + fast shutdowns via control+alt+apple+eject it works as expected.