I suggest DSP-based active crossover, time alignment and room correction hardware and software such as Danville Signal dspNexux, miniDSP or DEQX
- Time Alignment in 5uS increments
- Sample Rate Conversation and Jitter Attenuation
- Room Correction and Bass Management
- Active Crossovers
- low pass the subwoofer and high pass the full-range loudspeaker
I use two 15” sealed Rythmik subs in a very difficult room with great results attributable to DEQX. Use a professional (Larry Owens) to calibrate the DEQX and plan on spending three hours of your time.