[ubuntu] How do I hook up my old Acoustic Authority speakers?

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http://ubuntuforums.org – I have some old Acoustic Authority speakers (left, right, and sub woofer) that I want to use with my new Wild Dog. However, when I plug the "lime green" plug (only plug I have) into the "lime green" socket, I only get left and subwoofer. Do I need to get an adapter to go from my single plug to 2 plugs (green and orange?)? (Hardware)