[strokeZ]

Have some concerns adding an aftermarket HU....hope someone can help..

Have Alpine HU with 3 sets of pre-amp outs.....also has 18 Watts/Channel rms if taken at the harness out. A few things dont make sense to me.

1. after market bezel and antenna are non issues.....available and seem to give reasonable fit.
2. after market harness hooks into head unit via HU harness....but should this not be attaching to the pre-amp outs? read several threads here and seems that going from pre-amp outs will work if you can tie into vehicle specific harness - not sure how to go from RCA to harness.....nothing on line available it seems. Going from HU amplified signal to vehicle amp seems dangerous and / or useless as there is nothing to reduce HU amplified signal to a line level signal. Any one have similar experience in successfully doing this?

I see using the after market HU at pre amp outputs very advantageous for the following:

1. can use sub pre-outs to separate amp (replace factory woofers in floor area and rear deck) and drive subs w variable crossover on new amp to optimize sound and volume (use same wiring as in vehicle, just clip it from factory amp for new amp in/output)
2. Can use hi pass filter on after market HU to minimize low frequenciees to mid and hi range speakers. This would also unload factory amp as no low frequencies would be amplified (even tho not used).
3. will maintain factory amp for radio reception.

I figure pumping 4 new 6" subs w a high quality (JL Audio or equal) 75 watt / channel amp will do the trick

Any flaw in my logic? any electrical issues with this set up? (BMW's are finicky).......

glad for any help or thoughts that anyone can provide