What receiver do you have? Would be the first question...
As Sheep mentioned, most all DSPs should give you some sort of surround in the rears. Pro Logic sends the same signal to both rear speakers unless there is Dolby Surround encoded material being played, which is most likely what GIX is referring to. PLII does basically the same thing, but has parameters that allow you to adjust the sound to your taste and also does a much better job than the original PL. PLIIx can simulate separate channels for each of the rears for up to 7.1.
All channel stereo copies the front speakers to the rears and blends the mains to the center, so you don't get surround, but you do get a lot more sound, and it sounds like this is the one you're after GIX. If you want "true" surround, you'll need to use a player that has a digital connection to a surround processor (or use 6analog channels between two compatible devices) and play a disc with a Dolby Digital or DTS track.