Either use the 6-channel analog audio cable that was included with your speakers, or else use a 75 Ω coaxial digital S/PDIF cable (not included) to connect digitally.https://www.monoprice.com/product?p_id=2743
- I'd expect that the 6-foot length would be appropriate, depending on how far away your subwoofer is from your PC.
If your speaker system didn't already have the digital coaxial S/PDIF input, you could use an adapter
to convert to optical and use the toslink input. I don't know if adapters like that add enough latency to be perceptible.
i7-9700K, NH-D15, Z390M Pro4, 32 GiB, RX Vega64, Define Mini-C, SSR-850PX, C32HG70+U2407, RK-9000BR, MX518