WOW! Just connected my new Aego M's to my 360. Ammaaaaaazing 
I mean admittedly im going from my samsung HDTV's speakers to these, but still, I know good audio when I hear it! The clarity is amazing, fired up COD3 and was hearing stuff I never heard before, even at low volume! Cranked the volume up a bit, fired a gun and roared!
I'm still not entirely sure how i'd split the input to connect the line out of my PC as well as the phono's of my 360's VGA cable though? Those cables you linked dont seem to take into account the Left and Right phonos? I'm probably confused however.
Basically I think I need a lead with left/right phono plugs (into the sub) going to 4 phono holes/sockets (2x each of left and right) ? Is this correct?

I mean admittedly im going from my samsung HDTV's speakers to these, but still, I know good audio when I hear it! The clarity is amazing, fired up COD3 and was hearing stuff I never heard before, even at low volume! Cranked the volume up a bit, fired a gun and roared!

I'm still not entirely sure how i'd split the input to connect the line out of my PC as well as the phono's of my 360's VGA cable though? Those cables you linked dont seem to take into account the Left and Right phonos? I'm probably confused however.

Basically I think I need a lead with left/right phono plugs (into the sub) going to 4 phono holes/sockets (2x each of left and right) ? Is this correct?