Advice/suggestions for system upgrade

[vngrunt]

Hey guys, I am looking at spending around a grand to upgrade my system.
At the moment I have:
-Sony Explod hu 52x4w with 2xpre-outs
-Sony 6" 250w 3way front speakers
-Sony 6x9" 350w 3way rear speakers on shelf

I am after some advice on how my money would be best spent. Firstly, I'm after a sub in a box with an amp. I've realised from reading other threads that 6x9's don't go well with a sub due to cancellation, so what is the best way to overcome the issues that this brings, besides buying different speakers? I believe that if I hook them up to an amp I can filter out the low frequencies from the 6x9s??? Would this amp need to be connected to all four of my speakers?

Also, are tweeters added to the front a good idea for my system, to help with the high frequencies?

Would 2 extra speakers (eg. 6") in the back somewhere improve the sound in the car?

I'm not sure what crossovers are, would I need these?
Anything else that may improve my system for not tooo much money??

Any help or suggestions on what would be a good setup would be greatly appreciated. Thanks guys!

[garfa]

ok all a cross over (xover) is an inductor (to filter out higher frequencies) or a capacitor (to filter the highs), in its simplest form.
so what you could do is to xover the 6x9s with a cap to around 100hz. then you could have your sub and amp for the sub set up.
now the best way to achieve good sound quality (SQ) would be to get a good set of component speakers (splits for short). they are usually 2 or 3 speakers (2way or 3way) that are xovered so that each of the 2 or 3 speakers only handles a specific frequency range. so the tweeter gets the highs, the 6 inch gets the mid (and if its a 3way component set then you will probably have a tweeter 6 inch and 8 inch speakers). now there splits are put in the front because music usually sounds best from the in front and because there is less to obstruct the sound or the tweeters (the higher the sound the easier its stopped).
so dont worry about the rears, get either splits or at the least some tweeters for the front. then sub and finally amp the speakers.
for exactly $400 you can buy a good sub and amp. the sub and amp are both jaycar. for $400 includes EVERYTHING, eg: speaker, amp, wiring, crimps, terminal plate for the sub box, carpet for the box hollow fill for the box. the only thing missing is the wood. if you want to see the breakup of the prices then i can supply it and where to purchase all the stuff from.
that leaves $600 to play with.
with that i would spend $150 ish on a 4x50W jaycar amp. then the remaining $450 on a set of good 2way splits.
questions?

[vngrunt]

Thanks garfa. Your suggesting to connect the four speakers to a jaycar amp, and get another amp for the sub, right?
What 2way splits would you suggest I buy?
And where abouts in the front would I put the tweeters?
Cheers

[garfa]

yep. well do you think my break down of your $1000 budget is good?
if so, then i would recommend you go to a good car audio place (jb will not have anything near $450) and listen to a cd you know well that has highs mids and low notes in it.
and then buy the speakers you like the most.
subs are far less personal item really, the jaycar one pumps aparantly (i will have 2 in my car soon, i just need to/help with design of the box).
the tweeters will be put usually in the corner where the a pilar meets the dash.
anything else?