Amp questions

That head unit has separate preamp outputs for the fronts, rears, and subs, so you do not need a crossover.  I'm curious as to how your sub is hooked up now?  It should be hooked up to the non-fading preamp outputs on the back of your head unit--this way you can control the volume and cutoff frequency for the subs up at the dash.

What you need to power the other speakers is a 4-channel amp.  Assuming you just used speaker harnesses and the factory wiring for the front speakers and the rear components, all you need to do is run 8 speaker wires (positive and negative for each speaker location) up to the deck.  Cut the speaker output wires going from the deck, and tape off the ends going into the back of the deck.  Connect the ends that lead to wires going into the vehicle (or to a wiring harness), to those 8 speaker wires coming from the 4-channel amp.   You do not need to worry about the component speakers as they are run through their own crossover off of one signal output for each location.

Assuming a wiring harness adapter like the Metra 70-7301 was used, all you need to do is hook up the white, grey, purple, and green wires on the harness to the amplifier speaker wires.  Left front is white and WHITE/ black, right front is grey and grey/black, left rear is green and GREEN/ black, and right rear is purple and PURPLE / black.

Just a lil note:  sometimes amplifiers will have their speaker outputs listed as "A" and "B" or "1" and "2".  I always use A for the front speakers and B for the rear speakers, or 1 for the fronts and 2 for the rears.  Just make sure when you're adjusting the settings on the amplifier that you adjust the settings for the correct channels. 

Assuming you're talking about using  a 4-channel amp to power front and rear speakers, you'll actually use BOTH the front and rear preouts of the deck.  Thus you'll need two RCA cables.  The amplifier should have two sets of RCA inputs, and like I said before, they're sometimes called "A" and "B" or "1" and "2".  Doesn't matter which one goes to front and which one goes to rear, as long as you're consistent with how you do the amp settings for each set of outputs.

Ok first of all, wait and til you have the 2nd amp installed and running before getting a cap.  Cuz if your vehicle ends up having no problems handling the extra load, then there's no reason to get a cap and it will not really do anything for you.  I wouldn't be surprised though if your headlights start to dim when the bass hits really hard.  This is usually a sign that your charging system is being pushed to (and possibly past) it's limits, and you should take action.  That could mean upgrading the chassis ground cable that goes directly to the battery, or installing a capacitor, or maybe even getting a high output alternator.

Technically you would be best off getting a high output alternator rather than a cap.  There have been MANY MANY posts and discussions/arguments about this and some will swear by caps and some will swear by HO alternators.  General consensus seems to be that although a cap might fix the problem of dimming head lights, etc., by using one you're putting excessive wear on your alternator.

Now whether or not that means your alternator kicks the bucket at 10k miles, 40k miles, 150k miles, or maybe even not at all, is a totally different issue and one that can be argued either way.  Unfortuntately it's the kind of thing that's basically impossible "prove" or "disprove", and there's not just one right answer.

If you have the money, upgrading your alternator is the best way to go but not everyone has all that extra cash just lying around.  And it's up to you to decide whether or not it's worth that extra money to you.  If it is, or if you might add on more stuff to your system in the future, then I highly recommend upgrading your alternator.

If you don't have the money and just want a quick and relatively inexpensive fix, get a cap (1 farad will do).  Just be aware of the possible long-term side effects of using them.  But like I said, before you go and buy either one of these things, wait til your system is fully installed and see how your charging system handles the extra load.

There really are so many good 4 channel amps out there so it's really hard to pick a certain one, or even narrow it down to 2 or 3, without a lil more info.  Such as how much are you willing to spend on the amp?   Do you think you might ever add another set of speakers and another amplifier to your system in the future?

why are you waisting so much money on a car with so little value...  reminds me of waynes world..  i would suggest get a nice ride and then worring about everything else..

about the HO alternator.. its a really good idea..  i have one in my corrado and its great...  but why upgrade a car that wont last 100k miles..

optima batteries are a great upgrade...