Ok, here comes a big time pad recommendation. These pads:
https://www.aliexpress.com/item/33057605882.html?spm=a2g0s.9042311.0.0.27424c4d1ZGXiP
I had them lying around in the 105mm size and decided to try them while trying some different pads on the M1060C.
Since posting my mod in early May i've been looking for ways to further tune down the upper mids but nothing has really worked until now.
Here is a comparison graph that has the graph with the stock pads, with the sheepskin & pleather m1060c pads from the CP Yang store on aliexpress and these 105mm oval shaped pads from the link above:
(The graphs naturally include my other mods described in the previous post.)
These oval pads lift up the relative positions of bass and treble compared to the upper mids in particular. Treble detail is also improved. I also like sub-bass to be higher than midbass which is what the pads also give.
There were also two things I noticed about the stock pads after removing them:
1- They have a hard plastic frame between the pad and driver. This plastic frame causes ringing in upper mids (I could see this in the spectral decay waterfall plots, can post those if someone wants), so not having the plastic frame there cleans up the mids further.
2- The fabric sheet between driver and stock pads is actually not attached to the pads, so it can be easily used with other pads as well. After taking the measurements above, I decided to use it with the oval pads as well. It mainly reduces the treble peaks by a couple of decibels. I liked that so the sheet stays, but this is a matter of taste.
I only had this pad in the 105mm size as a leftover from my HF580 mods, so I haven't tested the 110mm size which has slightly different internal dimensions. Ordered one of those as well, should have it in a few weeks.