As far as I know the rather poor isolation is a design choice to increase the soundstage. I don't think changing pads will help much as they have vents outside the pads (the gap between the cups and the metal part).
Now for something completely different: Did anyone else try the TH900 with the Phonitor 2 yet? Mine came last Wednesday and I really like the combination: very detailed, massive but well-structured bass... very impressive. I used the A8 as a DAC.