You will need two 140XBE10000 Quantum backplane extender modules modules and one of the Quantum backplane extender cables listed below.
140XCA71703 - 3 ft, 1m
140XCA71706 - 6 ft, 2m
140XCA71703 - 9 ft, 3.1m

Note: You will need an empty slot available in each backplane for the Quantum extender modules.