Regarding the KLH 5 three position optional attenuation, it is not a gimmick, and purposed for your type of problem, i,e, the last sentence:
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In addition to upgrading its drivers, Geist overhauled the M5’s crossover, a 13-component network that uses iron-core inductors and Mylar capacitors. "The crossover is all 2nd order, 12dB/octave," Geist explained. "The low-pass woofer and high-pass midrange cross over at about 380Hz, low-pass midrange and high-pass tweeter at 2850Hz. The crossover is comprised of four inductors, four capacitors, [and] five resistors. Three of the resistors are used in the attenuation circuit for the switch located on the back panel."
Taking different-sized rooms and varying acoustics into consideration, Geist incorporated a three-position attenuator switch (marked "LO, MID, HI") on the M5’s backside (above a pair of gold-plated binding posts), a holdover from the original M5—sort of.
"The switch attenuates/decreases output above 400Hz," Geist explained. "I’m not a huge fan of attenuators on loudspeakers because of the affect they have on voicing of the loudspeaker. So, I repurposed the attenuator switch to deal with difficult room acoustics. The amount of attenuation is relatively small (0, –1.5dB, –3dB), over a broad frequency range. The idea is to pull some excess energy out of an overly bright listening room."
https://www.stereophile.com/content/klh-model-five-loudspeaker