UR 22 Not staying conected

I have an iMac 2011. I have the Sternberg UR 22 but it won’t not stay connected. When I boot up the iMac goes to internal speakers. Ive tried everything including re-setting pram and even re-installing Yosemite. Has anyone experienced the same thing?

Is there nobody at steinberg or anyone in the forum that can help me with this issue please?