Audio chain: foobar2000, Lexicon Alpha, ESI aktiv 10s subwoofer, M-Audio BX5 D3 monitors. Small, average bed(room), no treatments. Tried everything I can for months with hundreds of measurements: MathAudio Room EQ, IK ARC 3, Sonarworks, REW (with convolver foobar component).
I ended up with REW RTA optimization.
The BX5 D3 monitors "acoustic space" switch set to -4 dB (no, they are not in a corner or near wall, they are just most "flat" this way).
The lowest crossover frequency (50 Hz) is enough, this allows higher subwoofer level setting (for <100 Hz) without overboosting the crossover zone. The 100 Hz high pass filter engaged, for cleaner crossover zone and lower monitor woofer distortion. Subwoofer and full range peaks leveled out, and continuous phase set to where the crossover zone is most balanced according to RTA.