Relevant information first:
*Dell Vostro 200
*Realtek HD Audio onboard sound
*Driver version / codec: 188.8.131.5224 / ALC888
Alrighty, I'll explain briefly what the purpose is. I have my Xbox 360 hooked up to my desktop monitor using an HDMI cable and a DVI adapter. This works fine, and because the monitor has a VGA and a DVI port on it I don't need to ever remove anything to switch display modes (just gotta hit a button). Of course, there is no sound so to rectify that, I have the 360's composite cables hooked up to a composite->mono adapter. This also works, IF I plug this directly into my speakers (which is annoying because I don't want to have to switch input cables just to get sound from my computer or my 360). It outputs dual-mono sound and that is fine.
The problem arises when I attempt to plug the adapter cable into my computer's line-in or microphone jacks. It still plays the sound, but it's only single channel mono whereas plugging it directly into the speaker produces the desirable dual-channel mono. After several hours of investigating, I am no closer to determining if there is a way to fix this. I would much prefer a software solution to a hardware one if possible, just because it's not particularly convenient for me to go around shopping for cables and such. The Realtek Manager gives you no options to change from single to dual mono, if anyone has suggestions on how to get the output to be in dual-mono I would really appreciate it.