This would be the ideal a/d/s/ setup for an E46:
Source: Denon DCT-Z1 or Nakamichi CD-700II
Speaker Amp: a/d/s/ PQ40.2 (4x100@4)
Sub Amps (x2): a/d/s/ PQ40.2 (2x400@4)
Subs (x2): a/d/s/ R12s
Sub Amp Gain (x2): a/d/s/ AC50 spliced
Fronts: a/d/s/ 641is
Rears: a/d/s/ 346is
400 watts @ 4ohms supplying the front and rear stages
1600 watts @ 4ohms going to the 2 12s. (400 watts per voice coil)
There is something to be said about an install that is done with a "brand image" that portrays the ability of a brands products in a vehicle. It is hard to come by a company that makes everything "well", perhaps Diamond Audio or Pheonix Gold along with a/d/s/ can cover all the bases better than most companies.
Obviously if you wanted the best amplifiers go after some BRAX, Zapco, or McIntosh Labs amps. Full range speakers, audition Dynaudio and Focal. As for Subwoofers, and I am more into SQ (sound quality) than SPL (Sound Pressure Level), I would take a listen to some Alumapro Alchemy MX or RX subs. For source units: Denon, McIntosh Labs, Nakamichi (although they aren't very reliable), or the more gimicky brands such as Eclipse, Clarion, or the trusted Alpine.