I have the latest Lightroom CC with camera raw 9.1, updated last night. Great to see Lightroom recognises the new Canon 5Ds files, but when I try to tether with my laptop, the tether control panel alternates between recognising and not recognising the camera. On the back of the camera is a flashing computer screen image. Very weird. Hope you can sort that out.
It is too new to have tethered support, it will probably come soon.
You have an option to use a watched folder in Lightroom and another live view product such as the EOS Utility.
I was able to solve this. Lightroom needs the code from Canon, but you can download it yourself and apply it to the Lightroom plugin. I tested and used seccessfully on lrcc 2015.1
Should also work on other versions but I have not tried it.
Here are the instructions to apply the fix: http://jeffgardner.ca/Blog/?p=1023