actually, 4-6x9's sound really good. My cousin's Chrysler 300 has 6x9's like yours, but he upgraded to JBL power series and added 2x12" subs. The 6x9's handle 110 watts rms each easily, and he gives them 150x4 with an Alpine pdx 4150. It sounds great, won't win any staging or imaging contest, but it's super clean, and loud as hell...full range loud...not just bass. It sounds like a concert hall inside the car. It all depends on what you want.

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2004 300M SPECIAL
Alpine CDA 9833
Alpine Pxa-h701
Alpine Rux-c701
Rockford fosgate p400-4
Rockford fosgate p4004
Hifonics BX 1205D
JBL c608 GTi
JBL p693
Infinity 2.5" center channel
Alpine type R 12"(2)
all active SQL set up with 1900 watts rms