Question C/Sub not working

[1CoLoRz2]

Hello everyone, I recently picked up a sub and wanted to use it with my computer speakers. They are both plugged into my motherboard, the sub into c/sub and the speakers into line out. Windows and Realtek show that something is plugged into c/sub, and when I do the audio test with 5.1 on the sub works. If I plug the sub into the line out jack, it works. Any other time, it does nothing. Updating drivers didn't work.

Motherboard is an asus prime z490a, and the sub is a Klipsch k-100sw. Any help appreciated

 

[1CoLoRz2]

Bought a 3.1 splitter so they both go into line out. doesn't seem like the proper way to do it but it works I guess