Most domestic rooms do NOT need treatment, contrary to what you have read. Room reflections are important to natural reproduction.
Most people looking to treat rooms in fact have lousy speakers. Speakers appear to cause room problems in the bass when the Q is too high. This is prevalent as manufacturers and DIYers try to tune their enclosures too low, and end up with deeper but inferior bass. This problem is just rampant.
The next problem is speakers with a poor dispersion pattern. A good speaker will have an off axis response that mirrors the on axis response, but with an HF roll off. Whilst dealing with room reflections can improve a poor performing speaker in this regard, a much better solution is to replace the speakers.
I have to disagree with your comment that most rooms don't need treatment and I agree that reverberation is needed, but many rooms are too live, shaped badly WRT dimentional proportions and reflective vs absorptive vs diffusive surfaces. I also agree about bad dispersion patterns. That said, if hand claps in any room reveal echo, the reflections need to be dealt with.
My living room isn't huge, it's not a rectangle (it opens to the kitchen, a hallway and other rooms and the floor is carpeted. The system can't be centered on the front wall and a doorway is behind the right end of my sofa, with the kitchen to the right of my listening position. After I built the speakers with the crossovers you provided (thanks, again), I had a hard time positioning them without hearing comb filtering effects when I moved through the seating areas or walked through the room. The response in a non-reverberent space (outdoors, on a calm day, aimed toward nothing in particular and no hard surfaces) was measured and smooth throughout the bass through treble range, with the expected roll-off above the mid-upper 30Hz area (dual 6-1/2" Peerless 830874 woofers) and I'm not worried about the lowest octave as much because I don't generally listen to pipe organ or other music that demands the lowest extension and I don't want to disturb anyone.
I had made some panels to demonstrate their abilities for a home theater client a few years ago, so I decided to bring them up, to find out if they would help. I fired up Room EQ Wizard, positioned my mic and as usual, I saw a deep trough in the response in the 60Hz-100Hz range. I had tried changing the distance to the side walls, front wall, toe-in, distance from each other, distance to me, my position, height, tilted them back- nothing worked. As I brought the panels in, I started by placing one at the left and right walls, to catch the first reflections- the longer path length of the reflected sound adds enough delay that it's annoying, especially with percussive music, speech and vocal music. I also hear the reflections coming from the right and left speakers, from their opposite walls. I could treat them, but one is at a window and the other is the side of a kitchen cabinet. The first panels helped- I could watch the response change as I added each one. I then put a panel in the front corners and that made a major improvement. I added one to the left rear corner and saw more improvement and when I placed another above the first, it helped again. The last panel I had went into the right front corner and the whole time, I watched the improvements until the trough was gone. I moved the mic around the seating area and the trough never reappeared. I did spend more time positioning the speakers when I started carrying Parasound and installed the preamp and power amp, but the response has improved immensely since I placed the panels. I can now move around the room and in stereo (I don't have a surround system because of the layout- it doesn't lend itself to surround speakers), the dialog comes from dead center between the speakers, even if I'm past 90 degrees to the right speaker. The response sounds exceptionally even as the notes move through the musical scale, without causing fatigue. I rarely listen at high SPL (if I hit 95dB, it might have been one or twice, for less than a minute), but the stereo image holds up until I reach about 90dB, which is when I really hear the reflections on the opposite walls of the speakers.
WRT tuning too low, I specifically avoided that because I don't want the speakers to fall on their faces when the low end comes in but after seeing a TV show (Ultimate Restorations- you might like some of their projects), I found some videos with the pipe in Atlantic City that has 64' pipes and it reinforced the fact that if those frequencies are played through speakers without a dedicated mid-range driver or subwoofer, the mid-range frequencies will be terribly modulated when the lowest notes come in. These did surprisingly well, considering the frequencies involved. I'd really like to hear them through your system.
These are photos of the room where someone wants me to install a home theater- I did a rough measurement for RT60 and at some frequencies, it's >6 seconds, most are over >2 seconds. Terazzo floor, plaster on wood lath ceiling and plaster on brick walls with the brick attached to poured concrete. Not a typical room, but it needs to perform well.
