like the old skool sounding reeses bass noise,
yeah mix down needs work. what i usually do is get the bass and drums sounding as big and good together as i can, then work everything around them, starting with lead synths/ samples etc. get the levels right against the drums and the bass and eq to make sure theyre not getting in the way of the frequencies. might not be how everyone does it but it might help.
and as for mastering, it is something that is done AFTER a track has been mixed down ie finished and made as good as possible within the DAW then someone with lots of practice, lots of very expensive equipment, very good ears and a perfectly treated room (obviously all of that can vary but thats the idea) will tweak your finished track to squeeze extra life out of it.