lowpass crossover design

hello everyone. I have a 2007 honda civic. Currently it has an Alpine CDA 9884.http://www......com/item_10751_Alpine+CDA-9884.html as well as Boston Acoustics SC55's for the rear fill http://www.crutchfield.com/s_065SC55/Boston-Acoustics-SC55.html?tp=105 and a Kicker 8" dual voice coil sub also in the rear deck to operate as a midbass woofer. http://www.crutchfield.com/p_2061CVR84/Kicker-10CVR84.html?tp=111 The low end is filled out by two Kicker 10CVR124's with a punch P300-1. My dilemma is this. I only want to use the 8" for midbass duties probably between 70-100hz and the bostons pick up the rest. I want to run my amp http://www.crutchfield.com/p_204MGA465/Bazooka-MGA465.html?tp=115 to the Bostons as well as the Kicker and utilize the same rear channel for both. How can I provide proper crossover points to both speakers passively while still utilizing the same channel? So it would be Boston plus 1 channel of the kicker sub for rear left and the other boston plus other channel of kicker for right rear. How do I restrict the low end to the bostons while at the same time restrict the high ends on the kicker while still using the same channel. I need help with a passive filter so if anyone could help out I would greatly appreciate it. Juan