Tuning Subs on GenVs -- Help, Anyone?

I have a pair of GEN-Vs (with active subs powered by separate amp) and am having trouble tuning. The amp allows you to set the subwoofer cut-off frequency (up to 120Hz) as well as, subwoofer (relative) volume, and phase (the GEN Vs fire front & back, phase invert).
Anyone out there with sub-woofer -> speaker tuning experience? My main power amp is a Symphonic LIne RG7.