Using 2 sets of speakers on Win7: No other options besides stereo

So, I recently decided to retire my old Sony ICF-CS15iP speaker; but then I remembered I've been needing an upgrade to my computer speakers. It's nice on its own, but I have another set of 2.1 speakers also. I figured I could plug the Sony into the line in (blue) and the speakers in the speaker port (green) to use both at once, but that didn't work. I browsed a bit online, and was told to configure the speakers to be a different channel. Unfortunately, it doesn't seem I have any options besides stereo - on all devices. Yes, everything is powered and fully plugged in. I even went the extra mile to not use the jacks on my keyboard for the audio devices, but there's nothing doing. Is there any way I can still configure my speakers and Sony to work in combination, with the same sound coming out of both sets, or am I out of luck? Is there any programs I can download to force my speakers to work like that? They both have 3.5mm jacks, and I tried plugging them into the reverse of the intended setup, and even the panel on the front.
My audio card is an ATI/AMD. I can take photographs and screenshots at request.
Thanks.