How to wire amp to power sub and front co

I have an Alpine Mrv - f340 and I would like it to power my diamond audio M641 components (4 inch) in the front and a sub in the back (dont have a sub yet).  Crutchfield says i need a Tri-way crossover to connect to my speaker outputs to run the speakers in the front and the sub in back, however if you look at the picture of the crossover you'll  notice that theres only 4 wires coming out the opposite end of it that are for the left and right components, how do i connect the sub?  I dont know if anyone has ever dealt with one of these before but if you have i would appreciate your expertise. thank you.

Also it says on the crossover  "100hz or lower to mono woofer or subwoofer at 12dB per octave.  100hz and higher to left and right 6x9", 6.5", or 6" speakers at 6dB per octave.  Nominal impedance of all speakers 4Ohms.  250 watts rms.  Easy to install on the outputs of the amplifier."  

My speakers are 4's,  are they not compitable with this, they can handle 100 watts RMS so it seems as if theyd be all right.

my amp has an input selector with three settings: "1+3/2+4", "3/4", and "1/2"  which should mine be set to if i want to have all four speakers wired to the amp?  and what should it be set to if i want the 3-channel set up i described earlier?

I said all four speakers because i do not have a sub yet and i was planning on running my front components and back coaxials off the amp until i got one, sorry i didnt clarify earlier, and i was wondering what to put the switch on with that setup.  I looked at the manual and it is extremely vague when explaining the input selector so i just wanted someone elses opinion.  Anyway now that you bring up the crossover for the comps...If I have all four speakers wired to the amp, do i connect the speaker wires from the amp directly to the crossovers on the comps or skip it because the amp has a crossover, and when i have the sub and the comps running off the amp do i by pass the crossover for the comps or wire it in.  And i was wondering if you have ever seen an avalon with aftermarket components in the front, because the place where the stock tweeters are seem as if you cant put an aftermarket tweeter in there.  anyway thanks for your help.

You want to ALWAYS use crossover that come with components (unless you are bi-amping and REALLY know what you are doing.  You are not doing this.)

Connect the output from channels one and two to the inputs on the left and right component crossovers.  Connect the woofer and the tweeter of each component set to its output from the crossover.  Connect your rear coxials to channels 3 and 4 outputs from your amp.  Set you input switch to "3/4" which, as the owner's manual clearly states, "allows channels 3 and 4 to accept independent input signals."  Connect your front RCA output from your head unit to channels 1 and 2, and your rear RCA outputs to channels 3 and 4.  Turn off all HP and LP filters on the amp.  Carefully set your input gain.  This amp produces about 35 to 40 watts RMS per channel into 4 ohms.