You'll need an amp for your car speakers if you want to be able to hear it playing out of anything other than the sub(s). The tough part about this is that you'll have to wire all your speakers to another location than your dash (where the speaker amp you'll have to buy is going to be located...unless you can get one that is small enough to stash inside your dash), which will probably take a while and be frustrating unless your a seasoned vet, in which case you probably wouldn't have asked this question. (that wasn't an insult, Im an ameture for sure...)
You could probably get a 100w or 50w speaker amp off craigslist or on the internet somewhere for moderately cheap. You'd have run your ipod
into either a splitter for the RCA to send a signal to each amp, or (more easily you could) plug the rca into your speaker amp's input, and then from the output to your sub
anyways, I think it would be cheaper and probably quicker to just buy a decent pioneer
head unit...which will have the option to plug in both an auxillary chord and will have a usb connection w/full iPod control...since you have an ipod.Also I'd bet that you'll have better control of your speakers if sound quality is something you'd consider a must.
...but yeah, with some work and some money you could totally use your iPod, I think it'd be pretty cool actually, you could make the space your head unit was in before into a little secret cubby or somewhere to mount an ipod docking station...