OP, personally, I would tend to explore the rumble filter option last rather than first.
Have you tried messing with the sub-woofer bass contour controls? Mine are 4.5ft from the front wall but I still need a sizeable bass cut to avoid overwhelming the room. :)
The added benefit is that it stops the spikes and panel bolts from vibrating loose! ;^) :D
I think it’s a given that you probably visit the MLC website but if you do there will be plenty of good advice there as well.
Good luck!