How far can room treatments solve boomy bass?

Most likely you have one or several modes.
You can look in to a way of finding out.
Buy a XTZ Room analyzer pro II. It is complete and it'll show you exactly what is the problem. You can also use a Rives Audio PARC. The PARC is easy to set once you have the Room analyzer pro II. You just use the settings that RA pro II will give you, frequency, Q-value and level and feed it to the PARC. If you need to rid such modes most stuff will not suffice. You can also use Svana (diffusor.com) V-6 and V-4. These will do but they are large and very very heavy. I have used all most all Gik Acoustic panels, nothing will rid those low frequent modes. Not even the Monster bass absorbers (4 units) is anywhere near doing what the PARC does.
I use 14 Gik panels now (242,244 and TriTraps) and a PARC (measured with XTZ RA pro II). Best results you obtain by using both acoustical treatments and a PARC. I can assure you, this will take you where you need to go. You should now, bass modes doesn't only affect bass, it affects the whole range. You obtain better clarity, presence and PRAT. No lumpy swollen bass.

Walls create bass peaks. They amplify frequency (and multiples) that is f=1135/(2*L) where 1135 is speed of sound in ft/s and L is distance between front and rear wall (2 is for traveling back and forth in order to add). Larger room should help but you can also use sound absorbing panels. Normally they work the best when they are spaced from rear wall by either 1/2 or 1/4 (don't remember) of the wave (eqv. to frequency amplified by room). In my room it is not even possible and I'm forced to put them on the wall. I bought John Manville 817 rigid 2'x4'x2" (faced) fiberglass panels and glued them to fiber boards. I will stretch fabric on them and hang on the wall. Look at sound absorption coefficients: http://www.jm.com/insulation/performance_materials/products/ci9_800series_spin-glas.pdf

At 125Hz it is 0.38 - still OK but less dense (and more common) 814 is only 0.24. It is basically density (weight) of the panel that is amount of fiberglass they used. 4" panels would be ideal but I don't have space for them and there is, of course, WAF. Forget about curtains, blankets etc. If you can hear bass thru it then it won't stop bass reflections.

You can get much closer to unity absorption (which isn't a limit) with 4" - 6" of fiberglass. You don't want to overdamp the other frequencies, though.

The reason spacing off the wall helps is because pressure doubles on a rigid wall while velocity goes to zero. As you move away from the wall, there is a tradeoff between pressure and velocity. No damping occurs with no velocity -- therefore, spacing off the wall (or more thickness) is needed. At lower frequencies, this leads to ~ 6" panels to get effective absorption. Bass traps in the corner become a viable (if unsightly) alternative.

Have you tried tuning your speakers with the ports?
Rolling up a soft piece of cloth and loosely putt it in the ports will help controle the bass of the speaker.
You may have some bungs that come with the speaker for this purpose.

Zmanastronomy, I've tried it but it has to be very loose fabric and it also reduces bass punch. I had more room resonances with previous speakers (two 6" woofers) than new (two 8" woofers). It could be that larger woofers deliver more sound direct (larger area) or it is just better speaker less prone to interaction with the room. Some of the smaller speakers with ports tuned to extend bass have hump on the multiples of port frequency - visible on frequency response chart.