X-Server configuration with more than 2 external displays (on Ubuntu 16.04)

Connecting more than 2 external displays results in the displays being recognized but not configurable. From technical analysis done so far, it seems that the X-Server auto-configuration/-detection cannot handle this.

I guess that a manual configuration of the X-Server and amdgpu driver needs to be set up.

Has anybody already done this or is successfully running more than 2 external displays with Linux?

Any information is welcome!

Background info:

I have been going through this with Dell Pro Support for several weeks now. I could configure 4 external 2k-displays on a DP1.2 MST-hub running Win10, but only with the AMD Eyefinity enabled. Without Eyefinity a maximum of 3 external displays could be driven independently. (The laptop main screen is always running on the intel OGD.)

On Linux, more than 2 external displays cause disturbing effects. For example:
a) On the MST-hub, one external display is recognized and the screen is mirrored on all 4 displays. The laptop main screen is independent (i.e. typical extended desktop configuration).
b) Any display on the HDMI-Port (onboard or on TB16-dock) is recognized but never gets out of standby mode.

Currently I am running 2 external displays, connected to the DP and mDP ports of the TB16 dock. And that is pretty stable.

I have extensive debugging output available on request.

Dell Precision 7710; AMD Firepro W7170M; Ubuntu 16.04LTS kernel 4.8.0-58-generic #63~16.04.1-Ubuntu SMP; MST-hub: Club3D CSV-5400