Thanks guys! this is amazing! everyone is so helpful!

I will try to keep my stock deck for now... I might invest in an audio control unit... not sure which one will allow me to have adjustable crossover, Line out converter, and something that will raise the voltage to the amps.

I currently have no amp... I only have the sub, aux-in for my ipod on the factory deck, and one david navone LOC...

I tapped the rear headunit preout wires for my LOC. should I be tapping the front ones instead, so when I don't want to hear rear speakers my sub will still play?

is that the right place to tap the signal? just before the amp??? the wires known as Headunit output? its a clean signal and I don't think its being amplified.

does the Harmon kardon alter EQsettings to reduce distortion as I raise the volume?

The DVA-9861 is a single DIN unit...I'm waiting for mine to arrive any day now :)

You don't need to raise the line voltage coming from the deck, it's nearly 11 volts at full output.

Something to consider or share with your installer about the factory system:

It's active. Front left and right midbass have their own amp channels. Front left and right highs (2" midrange and minitweeter) have their own amp channels. Rear left and right midbass have their own amp channels. Rear left and right highs (2" midrange above the sidepanel armrests) have their own amp channels. The 6 by 9 " rear "subs" (laughable) have a mono amplifier built into the plastic containment module under the rear deck. Keeping the factory amplification is a BAD idea. There is both active cross-over and EQ functions built into the factory amplifiers that match up with the HK speakers. Using a "good" set of speakers with these amps is counterproductive. (I have tried this BTW, that's how I found out this stuff) You wouldn't mix and match Alpine speakers with a Focal X-over for example. Also, the factory amplification modules and speakers are low impedence. I've tested the drivers with LMS for kicks, and they were well below 4 ohms. (Nearly 2 ohms nominal) Throwing a set of 4 ohm components on the factory amps is going to roughly half their power output, and it isn't that great to begin with. Part of why the active EQing is nessesary is because of the high driver efficiency pushing close to 94 db @ 1w/1m. (Undamped paper cones) The DLS A5 is the simplest solution to high quality playback in your car IMO.

Here's a fairly old How-To that I used to help me with my car back in 2002:

http://e46fanatics.com/faq/stereosaga.html

The output from the deck is a full range "balanced differential" signal. The signal before the amplification is identical front to rear and is EQ'd by the deck adjustments. If you are going to tap into the deck output just BEFORE the factory amplification module, be sure that the device being used is capable of recieving a "Balanced Differential" signal. There is a difference between "Balanced" and "Balanced Differential", they are NOT the same type of signal.Again, using the front or rear signal from the deck won't matter. (It will be affected by your fader though)

I would NOT tap into the speaker out connection on the factory sub amp to drive an aftermarket sub amp. (Using a speaker level input on the aftermarket amp.) The signal is crossed over to match up with the factory speakers. I've done this myself with a single 10" sub in my trunk, and was not happy with the results.

Keep posting your questions and progress, we're all here to help you.

Adam