So I would still like an answer here, BUT
In my specific case, I learned that HDMI cables are not all equal. There is a thing called ACTIVE and PASSIVE on the connectors. Mie had no adapter, just the cable HDMI-DP. Apparently it was passive, and so it was not able to see each other. IF it was active it would have worked. My solution was to use HDMI-HDMI, and that worked to.
I would still like to know the limiting factors on # of monitors. with docking stations, people are wanting more and more.
