HP Z27q 5K seen as 2 Separate Displays

[toastedpayne]

Hey guys,

I've been having a real go at getting this monitor (z27q) running at 5k on my new build, but I just cannot get the full 5120 x 2880 out of it.

Every other snag has been ironed out: sound, video, wifi, bluetooth, sleep/wake with relatively little trouble from what I had been expecting from reading other posts in this forum. This monitor, though, may be my build's Achilles heel; although the 4K is working properly at retina quality 2048 x 1080 (which is fine for daily tasks, but defeats the purpose of having a 5K capable display).

After connecting the second DP cable and selecting what should be retina 5K at 2560 x 1440 I get actual 2560 x 1440 crap resolution and El Cap is recognizing two z27q displays: 1 at 2560 x 1440 and 1 at 2560 x 2880.

So here's what I've tried:
Every combination of the three DP ports on my gpu.
I've messed around with mirroring and changing through some optional combinations of resolutions that force the monitor into 5K mode but with some horrible split screen, scrolling screen, flashing, and color reproduction issues.
I've checked for and found the correct display override for this monitor that now comes with El Capitan.
I've played around with SwithResX with no success (although I feel I may need to look into that software some more)
I tried the iClarified display override (which caused a black screen)
I made a windows 10 install on a spare drive just to check that the actual hardware is functioning properly: 5K is glorious on the windows side.
I've switched to SMBIOS MacPro 3,1 and 5,1 and iMac 14,2 and 15,1 but the display is always seen as two separate monitors.

I'm just out of ideas and there's not too many posts regarding this specific display; I'm just hoping someone in the community may have some other tricks that may be worth trying.

Specs:
MacPro 6,1 SMBIOS
OS X 10.11.4
Intel 5930k processor
X99-Deluxe mobo
GTX 980 TI graphics
4 x 16gb DDR4 ram
512gb Samsung 950 Pro M.2 ssd
and some spare internal and external drives for extra storage

 

[toleda]

nv_spanmodepolicy=1 y/n?
See Post #1, 5K Resolution (5120x2880) via NVIDIA Drivers on Dell UltraSharp 27" Monitor | tonymacx86.com

 

[toastedpayne]

nv_spanmodepolicy=1 y/n?
See Post #1, 5K Resolution (5120x2880) via NVIDIA Drivers on Dell UltraSharp 27" Monitor | tonymacx86.com

Yes, I knew I forgot to list something. I've used that boot argument for each of the smbios I have attempted thus far.

 

[LostVector]

I can't get this monitor to work in Sierra either. I can tell you that on a real Mac Pro 2013, the second DisplayPort in on the monitor never enumerates as anything when connected. It somehow knows to ignore it instead of treating it as a real input. So the fact it is showing up as a second display is already kind of wrong.

One thing that makes the monitor slightly easier to use in the meantime is using SwitchResX to set the scaled resolution base to 3840x2160. This makes most of the "normal" scaled resolutions appear. I can use it at 2560x1440 HiDPI and it still looks a lot better than a regular monitor because of how high resolution the 5k monitor is.