start with this: http://www.lake.com.au/Lake_Contour.htm
this puppy has two XLR inputs, presumably from your subwoofer left and right outs (though you could also feed it subwoofer and LFE out, whatever, it can work from two inputs or one input and create almost anything you want).
Anyway, Bruce loaned me this puppy for evaluation (he is a dealer for Lake), and I am in love with the accuracy and capability of this EQ. After using pro audio junk like Ashley’s, I really appreciate a well done DSP based EQ/crossover.
So, this Lake takes in my subwoofer left and right out, sum’s them into a mono signal (at my request), and then splits out 4 signals for the two fans, the XS, and the left and right Watchdogs.
You can adjust the crossover points, filter shape, add EQ up and down anywhere, add phase adjustments, delay time, etc… really a very powerful unit.
Their new flagship EQ (about $5k) has extremely low THD… the unit I am looking foward to buying for myself.