I don't know your setup, but if possible I would run two sets of interconnect cables from the preamp, one to main speaker amp and the other to the subs.
A few questions that might help us, how much power is your Hypex class D sub amp and how does it's crossover work as far as input capabilities and adjustment?
A few questions that might help us, how much power is your Hypex class D sub amp and how does it's crossover work as far as input capabilities and adjustment?