I have my onboard audio set to 5.1 (analogue), BK plugged into the sub out and stereo headphones plugged into the normal stereo out port. I then untick the 2 rear and center speakers in the realtek control panel which forces those channels to be outputted to the font L/R speakers. Essentially 2.1 stereo mode.
I have the high frequency cutoff enabled but the dial all the way to the left. I set the buttkicker intensity to 12 when I power it on.
I find these settings pick up all of the station lift thuds and motion, the 'clunk' when landing on a pad, hardpoint deployment and firing, frameshift drive charging, glide mode rumbling, boosting and general engine rumbles as you accelerate / decelerate.
I also made an app so you can fine tune certain aspects and build profiles for different ships. It only works with audio devices which show the sub channel in Windows Speaker Properties, under 'Levels'.