Another way to reduce bass, open up the top end and increase the soundstage is to add a layer of self adhesive felt cut into rings and add to the outer edge of the housing underneath the foam. (this does also require slightly bigger foam, I got mine from Maplins in the UK for about £3.50, but should also be 'quarter' modded).
The action of this is that the speakers are pushed further away from the ears, naturally reducing the bass bloat somewhat and adding more top end (and soundstage).
I added 3 rings of felt giving about 4mm of distance between the iGrado speakers and ears.
The only way to take the sound quality of the iGrado's any further would be to re-wire the headphone cable.