[SOLVED] MSI RX560 Success, but unable to use DP and HDMI together

[colonelmustard]

Hello peeps,
new on this site, and not hugely teck savy.
I upgraded an old macpro4.1 to 5.1 with 48GB ram, SSD and a Radion RX560 4Gb - the goal being to run audio DAWs (logic - Pro tools etc) on 3 monitors. So no gaming but need 3 monitors for film score work. Installed Mojave. Works fine ... except..
Problem: I Can't seem to get more than 2 monitors at once.
Currently have - (i) HDMI- HDMI cable (ii) DP - HDMI cable and (iii) DVI - DVI.
When I try all 3 I get one of them (usually the DP -HDMI monitor) going black saying "no cable connected"
Please advise oh wise ones....

I've been researching this for a while.. to no avail.. hence my post ...
apologies if its been covered in depth elsewhere..
Could it be:
1. Power supply to card: Needing 2 cables and not just one cable from mother board. Thinking the extra current draw fro the 3rd monitor might need that 2nd power cable...?
2 . Port issues .... Framebuffer patching?? if so can someone please guide me though this as if i'm a 9 year old child, as I have no idea where to start.
3. Active /passive cables - they are all currently not active.. What cables if any should be active?

if anyone could shed some light on this i'd be really grateful

 

[carpman]

@joeblough
Apologies for digging up this thread, but I just got myself a nec spectraview reference pa301 30" monitor which can run at 2560x1600, but the max i can see in display settings is 1600x1200?

You have an old system with the same motherboard as me and was wondering if and how you got it running at 2560x1600?


Using clover to boot, with rx560 4gb dual-link DVI cable from rx560 to monitor on Gigabyte GA-Z77X-UP5 TH

config attached

many thanks