I install car stereos for fun. I\'ve done it countless times. $500 for the speakers and stereo install is not a bad price.
Its not a hard job, its just time consuming, and we all know time costs money.
At any rate, the Diamonds are nice speakers, MB quarts have always been a quality speaker. May I recommend Boston Acoustics. Everyone hears a bit different, thats why there are so many different options. But Boston Acoustic speakers are some of the best I\'ve heard. I am currently running components up front, 2 6\' boston\'s in the rear, and 1 12inch Kenwood sub in the rear. Just enough bass, but I could use a little more.
Its all about your amps too, getting a nice clean signal and a nice clean amp is very very important for reproducing a nice sound. I am currently running an XTANT amp for my highs and a kenwood 401m for my sub. The Xtant amps are awesome, again, they produce a really clean and refined sound that can\'t be found in lesser amps like sony and jensen.
I would suggest getting components up front 4 or 5.25 with seperate tweeters for the highs - Nothing beats that system.
Forget about the 6x9s - go 6 inch in the rear, you don\'t need that tweeter in the middle of the speaker in the 6x9 in the rear. The rear of your car is supposed to be fill, you don\'t want sharp highs comming from the rear.
And ignore all the haters, they are just jealous. Having a good sounding stereo in your car is one of the most important things to me. I spend many hours in my car, driving to work, driving back and forth from Philly to Boston. Its important to have a nice sounding stereo. I am not talking about bass that can shake the foundation of the world either, that is dumb. But I listen to a lot of Drum and Bass, and having a nice deep bass response is very important.
Here is a directory of pics of my stereo installation - I installed this all myself.
http://www.doodmonkeyradio.com/audi/pics/stereo-inst-4-02/Pioneer DVD head unit - XM radio - Xtant amp - Boston Acoustic speakers - Kenwood amp - 12 disc changer - PS2 hook up - Lap Top hook up-
Best of luck to you, any more questions and I will help best I can.