Ok a couple of questions on some speakers and then amps / capacitors hooking everything up and that stuff. I saw in another thread someone reccomended Eclipse brand to someone looking for speakers under 100. That is about the range I am in.

I saw the Eclipse and also some Infinity Reference and they were running in the same ballpark. The Eclipse where 4 way speakers it said with a 75 rms the Infinity reference were 3-ways at 100 rms. Opinions on these anyone? Are they both gonna be pretty good? I am not an audio junky and I cant really tell the different qualitys apart to well so if they are close I will just get what ever I can.

That is for the backs. Pretty much the same question for the fronts though. Infinity Reference or Eclipse.

Now for amps. Should I have an amp for my 4 main speakers? Like get one of those 4 channel amps that have 4X100 rms? So I can power them all. If so I also noticed on those that they have either 2 ohm or 4 ohm settings. How do I know what to put them at or do the speakers and amp do that automatically for me?

I have 2 Infinity Kappa 10in subs from about 4 years ago that I was thinking about using. I am trying to decide if I just want to use one though. I have a no-name brand amp that I was using I think it might have been BOSS or something. Should I just get one of those mono amps instead and run it straight only for the sub or subs?

I could run the two front speakers off the headunit and the back two speakers of a 4 channel amp and use the remaining two channels for the subs if you can make them into one super channel or something.

Lastly whats the capacitor for other then just storing up power (guess that might be it) and for my setup would I need one?

 

Infinity speakers tend to be more on the bright side if you know what I mean - more emphasis on the highs than mids. Eclipse speakers seem, to me atleast, to be better rounded where all the different frequencies mesh together nicely - neither bright or muddy. But it's all up to you. I'd try to find a local shop or local people running the speakers you're looking at and listen to them with the music you like; then decide for yourself.

It would be a good idea to atleast pick up a 2 channel amp for your fronts... As that's where most of the sound should be coming from - the front. Rear speakers are usually used for rear fill and turned down/faded so they produce a pretty minimal amount of sound. But once again, it's up to you - if you want your rear speakers to be loud too, go for it.
An amp with a rating of ~50x2 @ 4 ohm (if you're only doing the fronts) or 50x4 @ 4ohm would be more than sufficient for just about any speakers you want to run.

Whichever speakers you get will probably be 4 ohm (unless otherwise noted in the product description). Every speaker you buy/have has an impedence (ohm) rating. It has to do with how much current your speaker will draw from the amplifier. The lower the impedence, the more power the speaker will draw and the more power the amp will have to produce.
Most door speakers are rated at 4 or 8 ohms because running them any lower would greatly increase the signal to noise ratio rating on any given amp which could potentially add a lot of unwanted noise coming from your speakers. Most subwoofers are ran at a 2 or 4 ohm impedence since Class D amps are more efficient, and it's a lot harder to hear the unwanted noise coming from a subwoofer in the trunk hitting 25hz-90hz than it is with the nice set of speakers a few feet infront of your ears covering everything from 100hz and up.
The load on each channel of your amp is dictated by the rating of the speaker(s) connected to it, and how they are wired to it.
Some diagrams of different wiring configurations Lower impedence load on amp means less resistance in the current, so your amplifier is able to produce more power.

Infinity Kappa subs are wonderful for the price! I would definitely suggest running atleast one of them.
THE MOST IMPORTANT PART OF MAKING ANY SUBWOOFER SOUND GOOD IS THE BOX!
You could take the most expensive sub in the world, but it in a POS box, then take a $50 sub from WalMart build a box specifically for it, and blow the high end sub out of the water.

Boss = flea market junk amps. If you've got some nice Kappa's, they deserve a nice power supply.

Better idea would be to buy a 4 channel amp (50 x 4 @ 4 ohm), run the front speakers off of two channels, and bridge the other two channels to the sub(s).

Capacitors are total crap. Don't waste your money on one.
If you're having problems with drawing too much current (lights dim when subs hit, low idle when subs hit, etc.), a capacitor is like a crappy band aid. What you really need is a high output alternator to provide the amplifier with the amps it needs.

It's late, I'm tired, and that was a lot of typing so I hope atleast most of that makes sense.

 

So does that mean I need to run new wires into the doors so I can attach it to the amp? And dont headunits provide 50x4 to front and back speakers?

 

That's what I'd do. Whatever wire you get is bound to be better than what's already in there. Or you could just use the ones that are in there and just make it longer, i guess.

Head units have a peak power of 50x4 - their actual rms rating (the one that matters) is usually 12-22x4 and it's not the best [cleanest] power.