So, after looking at this very thoroughly, you're stuck.
You cannot drive all 6 speakers reasonably well, not at all really, unless you do things that will be absolutely pointless, like running the rear R/L doors and rear effects speakers in series so that you do not burn up the amp.
A little info on what Infinity refers to as their "true 4 ohm impedance technology": it's not really, and it assumes specific installation criteria that aren't in play here.
Infinity states that it's using a 2-3 ohm coil, and when it's used in conjunction with higher-resistance OEM speaker wires (usually 20-22 AWG), it's technically showing the amp a 4-ohm load, almost true but not applicable here.
Almost true but not really.
That said, the Sony amp is small, and it's also limited in how you can use it here.
You have very good components up front and good coaxial drivers in the rear doors, and the effects speakers in the headliner; let's talk about those first.
If you can return them, do, and here is why.
They can't be in play with the current amplifier, and even if you could, I would still avoid using them. They are decent, but they are not great; regardless of brand, it's just the limitations of the cone and tweeter in this particular speaker.
You have some good-quality polypropylene cones on the Infinity drivers that are uniform in shape, giving them a significant edge over the polypropylene 4x10s in the midrange frequencies, over the 4x10s, which are almost impossible to make where the cone is uniformly the same stiffness at all points, just not possible at $90 a pair. - and not practical if the retail on a perfectly uniform 4x10 cone retailed for $350 a pair; not enough market share to justify such a product.
More significantly, the Kicker uses a fairly inexpensive, narrow (extra-wide dispersion) PEI dome tweeter, and I'm just not a fan - of most any PEI dome tweeters.
Tweeters, especially ones in the rear, need to be identical to the ones in front of them, or they pull the entire sound stage backwards due to their differences in the sound signature (characteristics, think metal versus paper) the two different materials, shape, and sizes exhibit (their timbre, not timber), which is very undesirable.
Now the death nail.
If you could use them, on 45 watts, the Infinity speakers have a sensitivity rating of 93db; the Kicker is rated at 88db.
Even though the rears should be almost inaudible compared to the fronts (the rear is for fill, not for stereo or sound quality imaging), that 5db differenc in output, plus a 1 ohm difference in resistance, well that amounts to about 6db or almost 66% less ouput from the 4x10s than either of the other two, might as well not be there on 45 watts, likley you won;t really even know theyre on, comparativley, especaiily when you consider your already spreading that power distibution all around a large cabin, underpowering the entire syste,m it's a net sum loss, zero gain and only marginally better than the stock system.
So here is what I recommend instead.
If you're willing to forgo the rear 4x10's, then send the Sony back and get one of these, on sale right now for $118.00.
At 3 ohms, which is what those Infinity speakers are, this amp will output approximately 115-125 watts x4, markedly better and cleaner than the Sony; it's a no-brainer, and it's about the same size.
Just run all four channels to each set of F/R front and rear speakers (using the passive crossovers with the front components).
If you insist on using all six speakers, get the Fosi amp and consider running a bi-amplified setup, in an active/passive configuration.
Using the head unit and a few of the different amp crossovers, you can run all six speakers and have RCA signal output for the subwoofer you're going to get.
It's a rather complicated setup, and it involves bandpassing and splitting four of the six RCA channels from the HU out so that you end up with 10 channels of RCA outputs, but it would be a rather impressive setup and not break the bank.
On that configuration, your front midbass would get about 125 watts per channel, and the rear door speakers would also get the same; the tweeters would get 45x2, and the rear 4x10s (now relegated to actual rear fill) would see about 45 watts but on a narrower bandwidth of 80 Hz to 4 kHz, perfect for acting as effects or rear fill speakers.