Have you done any research into implementing a "distributed bass array"? Sometimes it is referred to as a "swarm".
It uses 4 subs, not 2. Pre-out left and right are sent to a crossover unit like the MiniDsp 2x4, where a crossover frequency is applied prior to the distribution to each sub.
With 4 subs most of the peaks and nulls created by your room are mitigated.
The improvement is amazing.