the above statement could be confused pretty easily. Here is how i propose you get 4 way.
Find a 2 channel amp that has a decent crossover that can lowpass to say 750-1000 hz , and a line output.
Connect midrange RCA's from the alpine to said 2 channel , set crossover on 2 channel to lowpass somewhere between 500-1000hz , 2 channel will be your MIDBASS AMP , connect the line outs on 2 channel to the set of inputs on the eagle that correspond with your MIDRANGE drivers , set the crossover to a HP of 500-1000 , then from then on out use your deck's midrange bandpass crossover to adjust the lowpass point for the MIDRANGES and the highpass point for the MIDBASSES. Then connect the tweeter rca's to the corresponding channels of the eagle and connect tweeters to it like normal.