Just did a brief comparison between the stock pads and two versions of my HM5 velours mod (one with just the thin red foam mounting ring, and one with an extra ring of thick, stiffer foam under the red, up against the cups). The stock pads have stiffer foam, a smaller opening and less depth. The HM5 pads with the extra foam rings were too tight, as one would expect. I ended up back where I started, and still happy. Then I listened to some tunes
No doubt the HM5 pads jack up the bass, and it can get a tad boomy depending on the mix, though I find that to be infrequent. It doesn't take away from the mids, as far as I can tell. The stock pads have less, but better controlled bass. They also have a tendency to get a little glaring or harsh in the mids/upper-mids. The HM5 pads tame that perfectly for me, and the extra bass is something I can live with, while the harshness is not. So it's a compromise. I'm sending 535 pairs to Capitol Hill. I think they could learn something from my mod
If I want more controlled bass, not to mention other things, I'll grab one of my other cans.
I got these to be fun cans for when I'm not totally focused on the music. For that I have the HE-560s. I tried the HD 650s, but found them uncomfortable (must have a weird head or ears) and less lively than I wanted. With the HM5 pads, the X2s have ended my search for go-to, easy-on-the-ears-and-brain dynamic cans.
I can see why people who are not bothered by the energy in the mids imparted by the stock pads would be put off by the added bass of the HM5 pads. If you're after softer foam and a curbing of a perceived glare, or just want to try something different for $20, can't recommend these enough.