Do not upgrade your system to the latest OS X 10.11 El Capitan when working with HDLink devices. Blackmagic Design hasn’t updated the drivers to sustain compatibility with OS X 10.11 yet.
Blackmagic-Design’s HDLink devices had a major update over the time. Due to their different technical capabilities, only the latest models are supported by LiveGrade.
You can easily distinguish the models by their housing:
Different model families of HDLink devices
Note: The displayed devices are only examples, there are different models within the family of HDLink devices. All models of the latest series of HDLink devices are supported by LiveGrade.
For more information how to setup your HD Link please refer to this articles: