[Yamikotai]

I'm looking for a way to get my 360 audio to input into my surround system, along with my PC audio; I have no idea whether this is possible or not.
My surround has two 3.5mm inputs, one for left speakers and the other for right speakers. Currently my PC audio is plugged into these. Now, that brings me onto my first challenge; would I be able to use something akin to a (well, two) 3.5mm splitter (or exactly one of those) plugged into each 3.5mm input on my surround, with the 360 and PC alternately plugged into them?

Would that work?

Second, I presume there is what I am about to describe, I just don't know what they're called; an adaptor for whatever phono plug the 360 has to 3.5mm?

[surgeVel]

Does your surround sound system not support optical audio? If it supports Optical/SPDIF, just get one of those cables and run it from the 360's AV cable. The sound quality is amazing through that.

[Yamikotai]

Unfortunately not; the surround I have is very high quality (well the sound it produces is anyway) but from the nineties. The only inputs are those two 3.5mm

Which reminds me; would I be able to just get a new subwoofer (one with optical and hopefully more inputs in general) and use my old satellites with that? That is of course if I could find just a woofer.

[Mak213]

Sadly there isnt much you can do. In a surround sound system, at least a high end one now, the Sub Woofer only has connections to be hooked up to a Pre-Amp or a Receiver. Most units now dont have the subs be in control of the surround sound system, other than those cheap $150 walmart units.

Having a limited connection base like you do, 2x3.5mm jacks, there isnt going to be any way you can do anything. The XBOX only can use the RCA or Optical. Your PC you might be able to find a converter. But no way yoru XBOX will connect.