wiring up speakers?

        I'm  still wondering.. and in a state of confusion.    I'm not sure if the high/low pass crossover in the Alpine 9815 works with the pre-amp out or speaker outputs or both.   Manual doesn't say.   Even if I use another amp for the 2 front speakers.. I still need to power and divide the frequencies among the 2 tweeters, 2 mids and 2 woofers in the soundbar off of 4 channels.  The sub-woofer will be off the sub pre-amp outputs.

To minimize your headaches, I'd suggest running your door speakers off the two front powered channels of the HU.  Then, using the proper passive crossovers for the 3-way sets in your sound bar, power those off the two rear channels of the HU.  Use the sub pre-out to drive your sub.

Yes, I know this HU.  It's rated at 60 watts X4 (peak) and the crossover (and EQ) settings control the signal to both the powered and the line-level outputs.

You don't think that the crossover in the headunit would be sufficiant for the 6 speakers in the soundbar? 

Also If I chose to use an external amp and crossover for the soundbar could I run both from dash speakers on the 4 channels of the H.U. if they are rated to handle the power?  What would the load be on the H.U. amp if the speakers are 4ohm?

The six speakers in the sound bar are two sets of three.  They are a stereo set of 3-way components.  The head unit is not designed to power a set of components.  It has high-pass crossovers that you can use to keep the low bass out of your main speakers.  For your sound bar you will need either:

A) a 3-way passive crossover for eact set of 3 speakers (woofer, mid, tweet.)  I am very surprised the speakers you have did not come with this.  Each crossover is then connected to one stereo set (2 channels) from either your head unit OR an external stereo amp.  Or:

B) a stereo 3-way electronic crossover and six-channels of amplification.  I do NOT recommend you try this if you are inexperienced setting up such systems, as it is very, very easy to overdrive your tweeters and mids and blow them.

Run your fron speakers off the front head unit speaker outputs.