Question : Problem: connecting 5.1 pc speakers to 5.1 home dvd player

I have the Logitech Z-640 speakers which are a 5.1 powered woofer and speakers. They connect to the PC sound card via the orange, black and green 3.5mm jacks (3-pole i think).
I'm wondering how to connect these speakers to a home DVD player with 5.1 audio. I have the converter that came with the speakers which converts the black and green jacks to the red/white RCA mixed audio. The only problem of course is that the signal is now 2-channel stereo instead of 5.1 surround since the adapter doesn't use the orange jack.
 
The DVD player (OPPO DV 970HD) has digital coaxial and optical out.
It also has 5.1 audio out (6 RCA jacks) labeled as follows:
CE, SW (black, black)
SL, SR (white, red)
FL, FR (white, red)

I think this should be a simple matter of buying a set of three 3.5mm stero mini-jack to dual RCA cables.
I'm just not sure what signal the black, orange and green PC jacks carry and if it is digital or analog.
Thanks in advance.

Answer : Problem: connecting 5.1 pc speakers to 5.1 home dvd player

your problem can be solved just by buying optical cable and  when watching from DVD player change the input to optical input on the control centre of the speaker unit.

This is the same stuff I do with my z-5500, which gives a great effect even with DVD palyer n playstation.