Third Monitor via DP-HDMI remains black

Greetings!

 

I request aid in the following conundrum:

I wish to use 3 monitors on my admittedly old Gigabyte 7970 (paaaatiently waiting for Vega). Not attempting to use eyefinity.

One of these is a projector connected via HDMI. Working fine.

The other two are actual monitors, one BenQ and one ASUS, both FullHD. They work perfectly on DVI and HDMI.

 

What does not work is connecting either of them to one of the two DP Ports on my card with this DP-HDMI cable:

https://www.amazon.de/gp/product/B01LYJYZBU/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

The screen is active, yet remains completely black for several minutes. After about 5min I can see the normal Desktop for a fraction of a second. After that the screen proceeds to randomly flicker on and remaining black 99% of the time.

 

I can confirm that the cable works by trying both monitors on my laptop (1070 in that one) with that cable. Plugged in, instant signal.

Is my old card just a tad defective? I have never before used those DP ports, but for certain reasons would really like to.

 

Current System:

ASUS Prime B350 Plus, BIOS 0803

R5 1600X

Gigabyte 7970 Windforce 3X

Win10 x64

 

Copy of current Driver:

Version der Radeon Einstellungen - 2017.0612.1651.28496

Treiber-Paketversion - 17.10.3211.1011-170612a-315159E-CrimsonReLive

Anbieter - Advanced Micro Devices, Inc.

2D-Treiberversion - 8.1.1.1599

Direct3D® Version - 9.14.10.01261

OpenGL® Version - 6.14.10.13476

OpenCL™ Version - 22.19.171.257

AMD Mantle-Version - 9.1.10.0189

AMD Mantle API-Version - 102400

AMD Audio-Treiberversion - 10.0.1.1

Vulkan™ Driver Version - 1.5.0

Vulkan™ API Version - 1.0.39

 

Thanks in advance for any tips.