I don't think you will find a driver or other software that will internally 'retask' the 3 jacks on the back panel the way you want (left + right stereo out on each jack).
Since you'll be connecting to amplifiers, why not use stereo out internally on the line out jack (green) and use 2 stereo "Y" adapter cables (male on one end, two female on the other) to physically turn that single output jack into three? Radio Shack sells this kind of adapter cables.
You not only get the 3 stereo outputs you want, but you get to use the other 2 jacks on the back panel for line (blue) and microphone (red) inputs.
Win 7 Home Premium 64-bit SP1, WA Pro 220.127.116.1181 beta, cPro MPxi_remix skin, 5.1 speaker system