well i'm not sure if this helps, but just to share.

i have a lcd tv with vga and component, so i decided to use PC with VGA and x360 with component.

for the audio, i just found out that my speakers (normal 3-piece; satelites and a subwoofer) have 2 inputs, so for the PC i just connected it like normal (from sound card to speaker). For the x360 however, i bought a stereo to RCA cable and since this cable was both males i just bought an extra RCA extender (which has both female sides).

so basically, i put the stereo end to the PC speakers, the RCA end into the RCA extender and connect the x360's audio RCA heads into the extender. works like a charm! all i need is to change source input on my lcd tv to view between pc and x360.