How far can room treatments solve boomy bass?

River251, for bass below 200hz try checking out the Cathedral Sound Panels. They are not absorption panels but instead work on the venturi principle which says that a gas moving through a small opening will speed up which in turn is related to pressure changes in the room from the woofers. To the drivers the room becomes effectively larger, acoustically. The frequency range of the panels is optimized by the size of the holes in the 11"x16"x2" panels that you install in the upper room corners. They control standing waves without rolling off the highs and are about 90 bucks each. I have not used them (I currently have the opposite problem you do, my 13.5'x15.5'x8' livingroom is largely open to the rest of the house), but I've heard others say that these panaels are the only type of passive room treatment that they use. Worth a look.

My experience tends to match what Phasecorrect wrote.

Monitors are perhaps a safer move. Assuming that people seems to go through acoustics half hearted. The risk with fullrange speakers (most often floor standers) is always that bass modes will be unavoidable and it cost some to get the bass modes an the rest under control.
Looking through some threads, also talking to acoustics that work this every day, has made me understand. None of the audio-bugged i have visited has done what is needed to make the environment nearly as good as the rest of the system.
Another bizarre thing here is cable dealers, who claims this can be solved with different cables. I guess a graph can tell each and everyone how much bass modes and dips can affect the whole frequency range. Basically, the room (environment) is as important as the system.

Any cable that corrects room response issues is seriously broken. Why do people fall for this crap?

The cable makers have to make such claims in order to justify the high prices asked for their products. But this is off topic.
Man I tell you boomy bass used to be thought of as a problem solved with few interventions and no fancy sophisticated acoustical analysis computer programs were employed. Has the OP tried any of the suggestions and if so what are the results?