paramoir
Formerly known as ImTheSmallKid
The sound is very slightly impacted, but for the better imo. A little more low end and because of more room, better sound stage. Honestly, the HM5 pads should be a required purchase after buying the M40x, especially if you are having comfort issues. For me it made the M40x go from pretty good to outstanding.
I know this is an old post but do you put the foam from the stock earpads to the hm5 pads or not? and what sounds better for you?