Regarding the "Doggie Treats" -
Dan caught me at the SF Bay Area meet, and installed the kit on my Alpha dogs, or at least the dots, and gave me the felt disks to try. I really liked the effect of the dots - they seem to remove the one issue I have, which is an occasionally sharp or hot spot in the sibilance range (I am very sensitive to this). I have listened further, and have decided the "dots" will stay in my headphones.
I was a bit more skeptical about the felt oval disks. I was pretty sure they would have too pronounced an effect. About the forth time they fell out of my headphone bag, I decided to try them. So far, I really like the effect. It is much more subtle than I expected. What I notice is a very slight reduction in the upper range, and a very slight reduction in efficiency. I like slightly rolled off treble, so this is a positive to me. The lowered efficiency (a small effect, but noticeable on my rig) is also a positive, as it makes it a bit easier to run on high gain on my Burson Soloist SL, if I choose to do so. I plan on keeping the disks in for a week or two, then pulling them out, just to compare again. I suspect not everyone will prefer the addition of the disks - they do roll the treble a bit. Great for me, great for many, some will prefer them out. It is nice to have the choice.
Just to be clear, sensitivity would be a more appropriate word here (the sound pressure level output at a given power level; e.g. 90 dB SPL @ 1 W). Since you're adding things in series with the headphone's drivers, you're basically dampening the sound and especially if you're using the felt discs, so you have to turn the volume knob a bit to get it to the same volume level as without the discs.