Connecting Xbox360 to PC (Linux)

Hey. Here's the setup thus far:

Xbox360 is connected to my monitor via the HDMI -> DVI cable. HDMI on the Xbox, to DVI on the monitor. That works well.

The HDMI cable plugged into the Xbox doesn't allow you to use the component audio (only 1 can be in at any given time) so I took off the plastic shell from the bulky component and now both fit. I have L/R audio coming from the Xbox.

I plug the L/R into a Y splitter and now I have a single 3.5mm audio male. Here's the problem..

If I plug it into the "line in" on my soundcard, nothing happens. It could be a setting in Linux but the option for Line In is not mute ..?

If I plug it into my speakers Aux jack, it sorta works. I say sorta because it only works if I take the 3.5mm jack going from the speakers to my soundcard out of my soundcard HALF WAY. It works if I ground the male jack as well, by having it touch anything metal, but the quality is best if I stick it out half way.

It's weird. I figure the aux on the speakers would be enough so that I don't need a PC or a soundcard to use the speakers.. since audio is being provided from the Xbox and the speakers are self-powered.

I'd like to be able to use Xbox audio + my PC audio without having to swap out the cables. What do I need? my PC is always on so it's OK if it has to go through the soundcard.

I have built-in audio on a GA EP45-DS3L but I also have an Audigy Gamer if that helps.