If you are NOT currently using an adapter, your display is working directly from Dual-Link DVI provided by the card.
To use the FireWire-400 ports on the display, you need to plug in the FireWire-400 cord from the display to the computer. The computer features FireWire-800 ports, the display wants FireWire-400 inputs.
When I hooked mine up, for FireWire I bought a small passive adapter (no longer available)
https://www.sonnettech.com/product/legacyproducts/fw_adapter.html
B H Photo (NewYork) and OWC.net (Illinois) still seem to offer adapters, under US$15.
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The reason these are referred to as 9-pin and 6-pin is Firewire-400 uses 6 pins, but Firewire-800 adds "push pull double-rail drivers" for better noise immunity at its higher speeds. (The ninth pin may be a shield ground for the entire cable, or perhaps one of the control signals is converted to double-rail logic as well) . To convert from 800 on the computer to 400 in the display, just provide fewer pins, done. The port adjusts automatically.