I know this is a noob question, but I have only recently started upgrading to serious audio equipment, one component at a time. I recently purchased a pair of M-Audio BX8 D2 monitors, which are connected directly to my PC with a mini stereo jack to dual XLR cable. I would like to connect my Lava LSP10 subwoofer to my setup, and I do not own a sound card and do not plan to purchase one just yet. Each of the monitors is active, and I am not sure what cable I should purchase to do so.
Use this, but not this particular one as this is crappy, but this should give you the idea on what to do.
1. Connect Headphone splitter to PC, connect your M-Audio BX8 D2 monitors as they currently are connected, using one of the holes in the headphone splitter.
2. Connect the Headphone to RCA jack to the other hole on the headphone splitter, Connect the RCA end to the subwoofers low level inputs.
Set the PC volume to where you set them, half would be a good starting point. Adjust the Monitors and subwoofers levels to achieved your desired sound. Once this is done, You would need to use the PC volume control to adjust the volume as this would adjust both monitors and subwoofer levels.