Taming bright Thiels

I have been attempting for months to find a way to tame the brightness on my 2.2's. Ended up with a crudely simple short-term solution after much tube and cable rolling and equipment fussing (System is Theta separates, ARC LS2b preamp, Rowland 1 amp, Harmonic Tech cables).
I experimented with taping thin material suspended in front of the midrange driver to produce roughly a couple decibels acoustical attenuation in the 1Khertz to 3khertz region from each channel. (I experimented with 1- and 2- ply tissue, cotton cloth, etc.)
What a magical difference. My wife immediately asked for a listening evening, something she hadn't done in over a year.
So I wrote to Thiel (many times) and asked if a low-value resistor wired in series with the midrange driver would have the same effect with less likelihood of side effects.
While they responded to every query promptly, they absolutely would not give any information on any possible modification of the speaker to attenuate its overly bright character.

Anyone attempted such a modification? Results? Caveats?