Try an isolation device under the sub. When I did this with my previous sub and turned the system back on, I thought I had forgotten to power up the sub. All the settings were the same but the boom was missing. This was a better tweak than the full wall of panels and bass traps I had at the time.
Also, the less expensive subs made me think I could never properly integrate a sub with the mains, be it monitor or floor standers. Having a quality sub changed that perspective. I run a JL Audio E112 now.
Good luck get set up. Usually winds up being an experiment of sorts.