I just got done doing the same thing you are currently doing, back in the day used alpine mostly, but the technology now is so much better, I helped my son put in a Clarion head unit in his mazda and a small subwoofer and amp to match up with the power on the head unit and stock speakers and was impressed. I recently bought a 2012 Scion TC, wanted a sporty 2 door with decent gas milage but not so weak that I couldn't get the car up to speed or pass someone...
Anyway, here I am 1,500 miles later and the system is almost completely done. Going with new gear is fine if money is a non issue but I'm telling you if you shop wise buying from local people cash, test and carry you can get some GREAT deals on some high end equipment.
Almost everything I have purchased to build my system has been done online through
amazon, websites, and the craig list local cash and carry!
Here's my setup so far and approximate costs:
2012 Scion TC
Pioneer Premium Touchscreen head unit that came with the car when I purchased it.
120 Square Feet of Stinger Roadkill Expert sound deadening.
Amazon.com 99.35 a box 36 sq ft, free shipping. $400 bucks (4 boxes)
JL Audio 300/4, 75x4 Amp for Front and Rears, Craigs list, excellent condition, Craig list local buy, $175.00
JL Audio 500/1 Amp for Sub, Craig List local buy, $150.00
JL Audio 10W6 Subwoofer, Craig List Local Buy, $200.00
Ported subwoofer box, $60.00 Bought new from local audio shop.
Hertz Energy 3-way components for the front, bought new from caraudio.com member in classifieds section $250.00
Hertz Energy coax rear speakers for rear, new $99.00 from local car audio shop
0 gauge wire for doing Big 4 upgrade, battery terminals, connectors, knukonceptz.com $85.00
Krystal RCA's, Karma 12 gauge twisted pair speaker wire, KnuKonceptz.com $90.00
Corner protector for sub box, $9.00
crutchfield.com
Home depot for heat shrink and other misc.
Fry's electronics for connectors.
The results have been astounding in my car, the dynamat/sound deadening to me is a MUST have, no rattles and the sound is so much tighter, bass/mid bass pronounced yet smooth.
The system has plenty of vol and the clarity is amazing, I will say over the past few months doing this I have spent some time and energy but had I paid a shop to install the dynamat, system, speakers, amps and purchased everything new online I would have spent a small fortune! So I have a great system, have saved some dollars and have enjoyed doing it myself to my own level of perfection...
So if your like me do your research, spend some time in audio shops, online, checking things out and go one step at a time. I've enjoyed the entire process, just about to finish up the project and really enjoyed it.