I had the same comment from FS a few years back about my Dodge Caliber.
Bullshit.
Specialized companies like Metra make dash kits with a special harness to allow the car's controls to still work, even though the head unit is gone. Kits like this one:
Pontiac G5 2007-2008 Car Stereo Radio Dash Kit complete - eBay (item 390123179030 end time Jan-24-10 07:28:20 PST). My car still has all the bells and whistles, even though the head unit is gone.
If you do go for a high-power sub (and with your music style, you will), then I highly suggest a capacitor so the car lights don't dim... ;-)
My car:
Dodge Caliber
Deck: Clarion ProAudio DXZ755MC
Glareshield speakers: Pionner tweeters
Front doors speakers: Pionner 2-ways 6x9
Back doors speakers: Pionner 2-ways 6x9
Subwoofers: Dual Clarion ProAudio XW1000 (2004 subs)
Enclosure: Q-Logic sealed
Amp (Front/Back): Orion Cobalt 430 (dates back to 1997)
Amp (Sub) Orion HCCA 225 @ 1 Ohm mono (dates back to 2000 - old school rocks)
Capacitor: PowerAcoustics 1 Farah
FYI, everything was bought used, except for the cap.