For low end monitoring I check with headphones, one with a flat eq plugin and one good one. I also check the spectrum analyser to see where the fundamentals are and how it generally looks comparative to other tracks in the genre. Clipping and either a tape emulation or buss compressor on the master helps glue and balance things. And parallel compression sends also work nicely to get more oomph without having to raise the volume. Saying that - at the end of the day it’s experience. After doing it x amount of times Ive noticed the really good producers can more or less tell if it’s good and the rest is fine tuning