OK, lets go back to the start. What surround system do you have? i can't believe you would just have a 3.5mm jack and an AUX input.
If you want to get to devices onto a 3.5mm jack input all you need is this:
http://www.amazon.co.uk/3-5mm-Speake.../dp/B0007OC96W
For the AUX, assuming it is twin phono connectors, you need is a couple of these:
http://incarmusic.co.uk/product/2054...-Splitter-Lead
But I can't help thinkthing there is a better way of doing this, like having the two on seperate inputs and just using the surround system to stitch between them. Are there no optical or digital inputs you can use? with AUX and a single 3.5mm jack you won't be getting surround anyway.