I have an iMac 27" 5K Retina (late 2015) with 32 GB, AMD Radeon R9 M395x 4096MB. I have just bought a second monitor, Dell Dell 27" UltraSharp UP2715K. I am running macOS Sierra 10.12.1.
Can someone help me...... When I connect my iMac to the monitor with the DisplayPort Cable (Mini-DP to DP) the Dell Monitor simply is black screen and on its way to shut go in power save.....
When I use 1 of the DisplayPort Cables along with DisplayPort Cable (Mini-DP to Mini DP) I only get 4K on my Dell...
What am I doing wrong? Am I not able to use this second monitor?