Z-640 5.1 and console audio

[Will013]

Not exactly sure if this is the right forum..but I figure it's the cloest..

I have some Z-640 speakers that I'd like to hook up to my xbox for some 5.1 surround sound for games..
However I lost the adaptor that came with them and Logitech has none they can send me, supposidly...
I was wondering what type of cable (and where can I get it cheapest) will I need to get my xbox to use these 5.1 speakers..

Thanks a bunch!

Will

 

[Will013]

would the xbox AV Adaptor work..then get a minijack to RCA, even though I dont see how I'd get 5.1 sound?

Or are there adaptors to convert 3.5mm jacks to RCA and use 5.1 sound, or at least all the speakers?

Thanks in advance,
Will