I've got a clarion vrx-766vd in-dash dvd headunit, with digital tv, and sat nav.
I've upgraded the fronts to 6.5" cadence cvl-6k components, 200 rms peak (quality speakers let me tell you), that inc's new tweeters.
Then i just got 5.25" polk audio components for the back, and finally two fusion SVC 12" subs.
Subs are running through an alpine V12 monoblock, and the speakers running through an eclipse 4ch.
People complain about weight and what not, but its illegal to go past 60km/hr in most areas (in australia), and in the event i take the car to the track, its not difficult to take out the stuff.
But i'd like to think i'm pretty serious into music, being a musician of nearly 10 years. I only really listen to DVD audio now, so quality is pretty important to me.
Alot of people really don't want to put all the subs and stuff in to save weight, but if you want to feel the beat, at least put one 10" or something. I didnt put 2 12"s in by choice, i got them off my brother, so no cost to me. admittedly, they came out of a sedan, so these things blow your socks off, but luckilly its complimented by quality front components.
I agree also, i'm not a fan of 6x9's they cover an interesting range of frequencies... The stock speakers were alright actually, but the bass was very empty, and the back speakers are horrible. tweeters are quality though!