i don't really understand your set-up or what yure trying to do, but to do a sub set-up correctly, i suggest an active outboard x-over between your preamp & two amps - one for the subs (get two subs for audio), & one for the monitors. i recommend the deluxe marchand xm-9 - a steal for the price - wery flexible & wery transparent.
good luck, doug s.