I lived in an apt. for a while. What I did was:
-- Use headphones when it's only me
-- Run the subwoofer "cool" [or off]
-- Have a "silly-high" crossover point [like 200Hz]
-- Keep the overall volume relatively low
-- Use "midnight" modes so there's not a ton of dynamic range in volume
Some combination of the above should work for all but the most cruddy neighbors ....
Of course my final solution was to get a house. Now I run things properly calibrated and at reasonable volumes and all is good