DS80PCI402: An application of PCIE redrive using with COM-Express Module（I7-6820EQ）

Now I want to use DS80PCI402 to transmit the signal of PCIE 3.0 with a long distance,but i don't konw what number of impedance should i control on the carried board.

Follow the COM-Express design guide,i shall control theTX and RX DC differential mode impedance to 85ohm ,but  follow the DS80PCI402 datasheet,RX impedance should be controlled to 80-120Ohm,and the TX impedanceshoud be controlled to 100ohm,i don't know how to match the impedance of 85Ohm from COME Module RX and the impedance of 100Ohm from DS80PCI402 TX,May I control the impedance 85Ohm at TX and RX on the whole carried board?Give me some advice,please.(And all other PCIE Redrive have the same problem)