When I bought the VGA cable, they gave me something like this.
At first, I just plugged that into the line in, and my speakers on the line out of my computer. But I found keeping my computer on problematic as it wastes a lot of electricity, and the noise of my PC fans. So I bought this.
I plug the 360 sound on one of the female connector, and the speakers on the other female connector, which ends up leaving that male connector out.
My idea was to plug the remaining male connector onto my line out on my PC, so I won't have to unplug/replug, but I keep getting the same problem, which was when I use my PC, my PC sounds would be very quiet, but the 360 sounds were normal. So now if I were to use my speakers for my PC, then I would have to unplug and replug, and vice versa for the 360 sound.