It seems like you've already done a fair amount of troubleshooting on this. I see several people on other forums(including nVidia) having the same problem. Have you already tried both the mini-DP and regular Display Ports?
If all else fails, maybe a call to Phillips might yield more help...
I ordered an adapter yesterday, still waiting for the item to arrive. Doubt it would make much difference since the two DP cables I bought didn't work.
Philips suggested some of the troubleshoot above. But given that without driver I was able to display 4k@64Hz, we can safely assume the screen is working as intended, so there's not much they can offer me :S