got 3 rca preouts from the hu rite?
front and rear out go to the 4ch amp, sub out go to sub amp
set high pass for the front and rear around 60hz, either on the amp or from the HU, not both
set low pass for the sub around 60hz, either on the amp or at the HU, not both
check the ameron sub is stable down to how many ohms. if stable down to 1 ohm u can connect the 2 dvc subs parallel-parallel. if not stable connect it parallel-series.