I have crossover questions

I just got the Alpine 9815 and it has a built in high/low pass crossover.  It has a 2 way switch and a 3 way switch.   I think that the 2 way switch is used with the 3 pre-amp outputs for front, rear and sub and the 3 way switch I think is used with the speaker outputs (4 channels) to provide 2 different sets of frequencies. (one for front and one for rear)  and using the sub pre-amp output only.   I'm not entirely sure about this as the manual doesn't seem to be too clear on this.   

Now I have 8 speakers total not including subs which  I'm not concerned about right now since they will go to the sub pre-amp out.    If you have an amp with built in crossover how do they usually get wired?  So the pre-amp outputs go to the amp for front and rear but how can you seperate frequencies for 6  different speakers if there is only 4 channels out?  Each channel dedicates a certain frequency to the speaker on that channel, right?   Help is appreciated,  thanks

Look man, I tried to answer this for you before, but I guess you didn't get it.

I highly recomend you use your Alpine 9815 in 2-way mode and use the proper passive crossovers for your 3-way comps in your "sound bar" connected to the rear HU outputs, with your door set on the front and your subs on the sub out.  But if you insist on using the Apline's internal crossover capabilities, here are the details:

In 3-way mode, the FRONT outputs (both RCA and the powered speaker outs) are the HIGH PASS signal for the tweeters.  The REAR outputs (again, both RCA and speaker) are the BANDPASS signal and are for the mid range drivers.  The SUB output is the LOW PASS signal and is for the woofers.  So the woofers for your comps and your subs will use the same signal and must be powered off an external amp.  Plus, since I do not think the HU built-in amps can support less than a 4-ohm load, you will have to use another external amp for the door speakers, and they must either be used as TWEETERS (connected to the FRONT RCA outputs) or as MIDS (connected to the REAR outs.)  See page 39 of your owner's manual.

Is this clear now?  If not, I suggest you take the vehicle to a professional install shop and GET HELP.

No, No I got it.   It's helpful.   Thanks!        I suppose there is several options here that I  can take so I will take some time to think and I know I will figure out something.   Just wanted to get the best results I could without breaking the bank  and buying several extra amplifiers.   Besides I got to learn this stuff cause I want to get a general idea of it before I go to school for it.   So thanks for you input.  

No problem I hope I didn't come off too harsh.  I do think you'd be better off and more satisfied with my first suggestion above.

What kind of speakers are your 3-way comps?