Ok finally ordered for my march 2010 production 325i with idrive and base stereo (6 speaker/no amp).
Equipment
DLS Reference R4 2-way component 4 inches
DLS Reference RA50 5 channel (4 x 70 W + 1 x 265 W class AB) The amp accepts high level input and has built in crossover. Channel 1/2 can be high and lo passed. channel 3/4 can be high passed and channel 5 can be low passed and has a subsonic filter.
Hifi rear shelf mid+tweeters (I had these from the speaker upgrade in my last car)
BMW OEM window sails
Setup
DLS tweeter tweeter in A pillar using OEM trim for a factory look.
DLS mids in front door
Factory underseats in parallel using 265w sub amp channel
Hifi mids+tweeter in rear shelf (because currently there are no tweeters in rear shelf on 2010 model)
The installer was recommend by the dealer. Paid deposit and ordered the components. Installation in 2 weeks because the OEM trim will have to be ordered from BMW.
According to the amp manual, the subwoofer output is 2 ohm stable. Two 4 ohm subwoofers can be connected in parallel so use the sub channel to power the underseats in parallel. This also allows me to upgrade to SWS or Morel underseats in the future.
Now I have 2 choices:
1) Active crossover the front 2-ways and use the factory head unit to power the rears. Not use the DLS crossover that comes with the fronts.
2) Use the DLS passive crossover and use channel 1/2 for fronts and 3/4 for rears.
Which should I go for? Any other considerations?