I'm wondering if instead of buying a splitter, I can just have the headphone and speaker playing at the same time.

I have a stereo system that sounds better than the pc speakers, but the bass isn't as good as the pc speaker's subwoofer. All i want to do is be able to plug in the stereo system into the front headphone slot while having the pc speakers plugged into the back speaker slot and be able to play both at the same time.

What would be even better, but probably not possible, is if I could hook the pc speaker's subwoofer up to the stereo system but thats probably a lot of trouble..

Is there a way that I could make the 2 pc speakers and the 2 stereo system speakers be recognized by the computer as a 4 speaker system? again, probably impossible or too much trouble.

You plug the stereo system into the rear channel and the PC speakers to the front channel (or vice versa) - that's what i have set up and it works just fine.

You need to fiddle with your soundcard settings to get it to run in 4 speaker mode.