I am using a single 6 channle amp now and with out having a sub-woofer output from the empeg It doesn't work right.

ie

if I set the sub input on the amp to sum channles 1,2,3,4 I get bass but the crossover doesn't function right if I use the cross-over on channels 1,2,3,4 to limit their bass to signals over 90Hz there is nothing to sum for the sub woofer.