gtx 980 and no boot screen

The Dells are both hooked up to the DP. I did buy the flash from Mac Vid cards but the flash is working correctly on lower resolution monitors. It is just DP only where they fail to show the bootscreen. This would seem to be a hardware incompatibility. The Mac edition HD7950 has the same behavior. It only shows the DP input after the boot has fully completed. I was hoping for some kind of terminal command that would maybe adjust the boot output parameters.

Yes, I will certainly throw the question to Chris at Mac Vid cards. The fact that the Mac edition 7950 shows the same behavior is an indicator that this is a communication with the 4k monitor issue. I am leaning towards either a 60/30 hz issue or screen span issue. When I try to use the gui to force mirroring it does not persist past the reboot. This Dell does not have a menu screen other than port select so I can't tweak from that end. I am praying there is a Terminal solution. I will report back what Mac vid cards has to say.

I have made more progress. I discovered that if I set the MST from its default "off" to "primary" then that forces a 30 mhz refresh rate(and mirroring) allowing the Dell 4k monitor to show the Apple boot on one screen. I can then select any one of my boot drives. When logged in, I go into mirror mode at 30 hz. I have to then go back into each Dell monitor to reset the MST to off before full resolutions, 60 hz refresh rate, and spanning can be re-selected. This is the best work around so far. The best would still be a terminal command that runs the machine at 30 hz/and or mirrored at boot as that way I would only have to deal with System Preferences. I did see a thread out there last week that did have terminal commands that affected mirroring but now I can't find them.

On second look, not so much progress as the menu button only shows up if you have signal so you can't boot up if you are running at 6O hz. if there is no signal on these Dells only the input controls will show up. So my only option to get rid of the DVI(or HDMI) monitor in the array would be to lose the sixty hz feature and only run them at 30. I still need a way to force OS X to be in mirror mode and/or at thirty hertz at boot startup.

Thank you for your response. Would were it that simple for me. My cables are already only 1.5. My issue is clearly that the low level boot screen is only thirty Hertz but these monitors don't pick up thirty autonomously. They are preset for 60 nrz MST from their menu. I need a terminal command to force the low level boot screen to output mirror mode.