How far can room treatments solve boomy bass?

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.

Have you tried repositioning your listening seat in relation to the back wall for the smoothest bass response and THEN positioning the speakers in the room? This is basically the method described by Jim Smith, author of "Get Better Sound". He did this in my room to great effect. I also have 16" Tube Traps, but the proper location for the listening seat (height and distance from back wall) is critical to good, balanced sound, IME.

Inpieces said it very well. Get some GIK Tri bass traps for the corners of your room. They stack on top of each other and go floor to ceiling in the 4 corners of your room.

In addition to these get one bass wall trap panel for the wall behind your listening position. Lastly get two 244 panels for the first reflection points on the side walls.

This will GREATLY improve your total sound top to bottom. Greatly!