I wouldn't buy anything from crutchfield., but you're getting the right idea.
What you need is something to isolate your signal output from the bose head unit into RCA's (this is debatable as I mentioned before, but it is what I would do.)
You will also want a crossover function, adjustable.
I would recommend a Memphis 16XO3, which runs $129. I need to do a bit more research at home (instead of work) for you, but I'll see what it does to verify if it is the best choice.
The Kicker 3-way looks good too.
I would recommend looking at woofersetc.com and sonicelectronix.com though, both of them have served me fairly well over the years.
From there, you'll need to run fresh wiring to the doors, which is "fun". Check out my install page link, found on my signature, for help with this. From there, its a matter of amps and maybe a sub. Forget about the rears, btw. Just leave them alone, and let the bose thing deal with it. Ideally, your front stage should sound so good that you don't need rears.