DuoMaxwell

**EDIT** After typing this I realized it's a novel and I've asked tons of questions in it. My basic question is on how to hook up my sound.
Ok well I'm currently working on installing a carpc in my car. Basically, I'm keeping this as low cost as possible (haven't even spent any money yet). I have an LCD screen (5") with RCA inputs and an S-Video input that is powered by 12V DC current. Basically, so far I have installed everything correctly and the LCD screen works.

So far I've basically stripped the CD changer and faceplate off the head unit, and mounted it slightly farther back, then put the LCD screen in front of it.

Sound: This is where I've run into a problem. The system as 7 speakers, two tweeters, and 5 mids/subs in various locations. I don't really know what to do for sound, I tried 3 separate FM Transmitters but they all come through with fuzz and, while I'm not an audiophile, I can't stand excessive fuzz. Now then, I need some advice on what to do, but here's the ideas I've come up with so far:
1) Use an Amp: I already have RCA jacks, and the daughterboard outputs stereo sound (two sets of red-black wires) so this option would be easy. But how would this work with those giant plugs (see #2) that the head unit has? Do those giant plugs have the wires that go to the speakers? I could just hook up a small battery and short those leads using the battery and see which wires are which speaker right?
2) Use the Existing Head Unit: The head unit has what looks like a MIDI port on the back but it isn't labeled and wasn't used as installed by the factory. Also, the FM antenna cable comes in separate and plugs into a small FM Daughterboard. The cable resembles a 1/8th inch headphone jack. Any possibilities of hacking there?
3) Buy a New Head Unit?: I could just go out and buy a cheap head unit with an aux-in but how does that hookup with those existing ginormous cables? Also, will I still have the same sound quality with the 7 speakers, along with base, fade, and balance controls? Finally, will my steering wheel volume and radio controls still work?

I'll get some pictures up as soon as possible. Sorry for the huge novel.

Thanks,
Duo Maxwell

**EDIT** I read the installing sound FAQ and noticed an "Aux-in" adapter that looks like a MIDI to RCA adapter. Where could I get my hands on one of those?