This seemed like possibly the best thread to post this.
I recently damped the midhorns of my H-IIIs at the recommendation of a Klipsch modder who swears by this tweak. It basically involves wrapping the midhorn in constrained layer bitumen sheets (think Dynamat). I used Stinger Roadkill brand, as back in my mobile audio days, I found its performance superior.
I do notice a slight improvement but it's not nearly as dramatic as was alleged by that member.
Before I catch flak for modding these speakers, please understand that I did so only because over the last 1.5 years, I've begun to detect some consistent weaknesses. Most notable of these is a coloration/chestiness to the midrange and vocals. These are $2K speakers after all, and in stock form, can't match the midrange clarity or refinement of the ~$3K^ speakers I've owned/auditioned. For example, my $3300 retail JMR Bliss Silvers trounce my H-IIIs in midrange refinement. So I figured the midhorn damping might improve this some - it has, but it's not a massive difference - definitely a slight improvement in lyric delineation and decay.
If anyone else here has tried this mod or similar mods, I'm interested in your feedback. I think these speakers can be taken a bit further but I'm not prepared to start swapping out drivers and such.