I am not good at electronics, per say. But if your 8 pins can fit into any 8 pin the PC has, like PCI cables or 2xMulex, first I'd check on the PSU to see the values you get, Amps and Volts. Check it's the same your chair needs, if it's not the same or very close, you might damage one or both of your devices.
Take into consideration that if any other devices are connected on the same rail as the specified cables from your PC, the values change. I'd google or read that.