let me add my 2 cents:

Boomy= alot of echo bass bouncing throughout the room along all feq
Muddy=dull un-define lacking tightness, They way most tuner cars sound, all boom.

Your sub should hit like a heart beat, not linger on or echo. Boominess can be results of room surfaces (hard floors/walls) and placement. Muddy is more of a poor sub driver/crossover setting itself, not able to give a tight response.

You should only really hear the sub when the action calls for it not during the normal dialog. Your sub is always working in a support role until its called upon to bring that chest pounding, window shaking, seat rumble effect. Then just soon as it hits it should jump back in its support role as if you never knew it was there.