trying to use a expansion chassis for the k80 will have the same issue as the z840,..... improper cooling
the k80 was designed for servers/systems where the cooling fans are able to blow air directly across the entire card and out the back at a high volume (CFM) no expansion case will be able to do this for one much less two cards
and you will also run into power issues as each card requires over 300 watts
you will have to use the telsa Cxx series or the k40c (note the "c") model which has the nessary shrouding/fan for a workstation that the k40/k80 lacks
please read the nvidia specs/requirements for this card, note the power and cooling sections for the minimum requirements
https://images.nvidia.com/content/pdf/kepler/Tesla-K80-BoardSpec-07317-001-v05.pdf