Some info that may help: The 1.6 crosses over the tweeter quite low, I believe about 800Hz if I recall correctly. So the resistor has the unintended effect of shelving down everything above this frequency and elevating the bass through lower mids.
In my room I have experimented with placement and treatment and have reached a compromise where my 1.6's sound full and warm and not at all bright (no resistors). However, most every time I try a box speaker in the same location of the Maggies (I am using the Cardas placement calculator and then fine tuning using REW) I am shocked at the amount of upper bass that I hear. Measurement confirms that the Maggies have a fair bit of a suckout in the 100Hz area, in my room at least, but this has been consistent for multiple rooms I have measured in. I have heard of people eliminating this issue with "wings" added to increase panel width, but have not tried it as I enjoy the freedom from boxiness that they have in this same area of response. Everywhere else I get really flat response down all the way to their 40Hz limit with the exception of a 46 Hz room mode that has the effect of making the upper bass seem attenuated because the lower bass is boosted. Experiments with equalizing out the single major room mode have always resulted in better sounding upper bass - now I just need to find an EQ that is transparent enough to use
Also note that the suckout is evident in a near field listening arrangement (8-9 feet from the speakers which are in turn about 5' from the rear wall). I have not tested far field as I hear too much of the room when I do this. Moving the speakers closer to the side walls may add some upper bass emphasis, but moving them closer to the front wall causes brightness to be elevated.
I use Hsu subs and their 24dB/oct low pass filter REALLY makes them easy to integrate. Set to 40Hz, measure, adjust level, forget. Other subs with shallower roll off cause more cancellation issues than they are worth.
On the topic of tone controls - I use a tube preamp with fairly subtle bass and treble controls. Bear in mind that common treble controls cut the region around 10KHz, so they do not address brightness which is really at a lower frequency (if you look at the Stereophile measurements, there is a small elevation in response between 6kHz and 7KHz on the 1.6 which MAY be the culprit, but I am not convinced that that isn't just a measurement technique issue as my estimation of brightness is that it is somewhere between 2K and 5K). Cutting the 10kHz range removes "air" and "shimmer" and does not affect brightness until you cut out so much of what is good that it starts impacting the area responsible. A sweepable parametric EQ would confirm this, but I have not tried it as I love the sound as-is.
Bear in mind also that a lot of the brightness issues exist in average quality recordings that have been poorly mastered.
Also play with toe-in - they don't behave as you might expect from a conventional speaker. I also added some beam clamps to the feet to provide a primitive leveling mechanism. Adjusting tilt back greatly affects perceived brightness at the seating position. I aim them to be just slightly tilted back from vertical for my listening position and it is important that they are set the same or imaging gets messed up.
