NO understanding of audio, cut harness--halp me make sound

[mechanicalmoron]

*editeded with update*

Well I'm in the process of installing a 2/3/4 channel switchable amp WITHOUT a head, with sony 5.25in round speakers in the front, and have a few more questions.

I have some old blown speakers that I was considering just duct taping the surrounds back into for rear speakers, but thei're quite large, like 6 by 10 or something. Since I'm only going to have 2 channels from a headphone jack going in, can I run them in paralell with the fronts, or will anything malfucntion or make funny noises or something? Will only the small speakers or speakers with less resistence play if I do that?

I also have a few random (non car) subs, can I wire a sub in somehow in parallel or something? Again, this is going strait from portable device into the amp, I'm trying to figure out a way to split it properly. Can a sub take the full spectrum of sound, and by it's electrical and acoustic charicter, only play the bass? Or will it make funny noises?

If I need, I could set up the input on a splitter, for duplicate channels. But I need to know, especially with the sub, what will happen with the speakers getting the signal with no head. All I know is I succesfully made primus come out of the amp/speaker, directly from my ipod, and plenty loud.