Sonnet has made a power cable for the Avid HDX card that is compatible with the Breakaway Box. The part number is TCB-HDXB and is available from Sonnet or Sonnet-authorized resellers.
If you are connecting from a DVI (or sometimes DP) port on your GPU Card--via an adapter cable--to an HDMI port on your monitor and the display looks magenta, you can fix the issue in the monitor control panel. Go to the monitor Color Settings; select Input Color Format; change from RGB to YPbPr. That should solve the problem.