Quick update on the YH-100s. The ID stretch on the R10 pads has been a huge success. Over night the cans evolved into YH-1000s! Well, that's a little hyperbole, as they still say YH-100, but I had the pads on empty prescription bottles about 35mm-37mm in OD. The ID stretched about 7-9mm and stayed about 4-5mm wider. Definitely enough improvement to bring up the treble and upper mids so the cans do not sound dark, while the bass is probably a little smoother and just a touch more balanced.
My mom is a quilter and has cotton batting scraps. I'm going to use some batting instead of the cotton balls and see if I can get the same sound with much better balance between the left and right channels. Oh, they sound good and you can't hear a channel imbalance per say, but I know it's there simply because I could weigh the material and the cotton balls very so much. The cotton batting will be much, much more consistent throughout the country and within the material itself. I am going to look for a small gram scale just so I can weigh the dampening and see how close it is. Since the fiberglass doesn't really dampen the drivers, then it not as critical, but a weight there would help too. I WON'T be removing the blu-tak to weigh it though. It was a PITA to put on and I cut the pieces as consistently equal as I could from the same extrusion, so they're as close as anyone's ears could tell.
Also going to change the dampening on my YH-3s to mimic the YH-100s and see how that sounds. They sound so closed in compared to the 100s now and I followed Ludoo's bass heavy scheme originally and needed more dampening.
EDIT: Just listened to the YH-100s against one of my favorite cans, cetoole's QP400s. The QPs are a little forward and a touch bright on the treble, but it's a very enjoyable headphone and probably my favorite can in my house at the moment if I had to choose just one can for all music types. The bass on the YH-100s is much stronger and the mids are there and sweet, just darker. So I think the 100s are still a tad underdamped for the R10 pads. Now he question is, do I add cotton or cover four holes on the driver?