I have an older set of 5.1 surround sound speakers from Logitech that I'd like to use with my Mac Pro, however the Mac Pro only has one port for audio out other than the Optical. The Speakers only have the three RCA? plugs in the colors Black, Green, & Orange and I'm not sure how to get it so that I can use all the speakers.
The Speakers:
The Plug:
Is there a compatible Soundcard I can plu into a PCI slot or is there another, better way to set this up without the use of a receiver/amplifier.
The Speakers:

The Plug:

Is there a compatible Soundcard I can plu into a PCI slot or is there another, better way to set this up without the use of a receiver/amplifier.