The display port adapter you are using is not a supported connected device which may be why you are not getting a steady picture.
I have an article here that will explain what devices we support.
Here is another article that explains how the supported devices work.
Hope this clears up your situation!
What do you mean by steady picture and sound?
Does the picture freezes? Or black outs? Or else.
If you get the picture but if freezes, it is most likely internet uplink problem in location where M2 is installed. Remember that most of internet providers advertise and sell downlink speed with much slower uplink which is essential to get quality picture on receive side. Even with 80Mbps downlink in Florida, you may not get proper reception if uplink on M2 side is slow.
Leave the displayport and hdmi adapter out of the loop as this is less likely to be causing problem as someone else suggested.
Provide the answer and we might be able to troubleshoot.