Personally I found that the dampening doesn't enhance bass, just takes out the glare in the treble.
The holes in the back felt didn't *seem* to do much but it might just be that all the other mods I made on my pair made it too hard to discern the difference the holes made.
I think maybe to get more effect for bass, instead of punching holes maybe you can remove the entire black felt-like thing around the drivers instead of just punching holes. Punching holes didn't make much of a diff on my already heavily-modded pair.
The mods I found that added a lot of bass were:
Pleather Pads.I found some Pleathers that I was able to wrap around the normal bowls, comfies or flat pads of the Grados. This *really* added a lot of bass.
Distancers -- adding distancers seems to enhance the bass response probably because of the greater space for the air to move. This works great with the Pleather Pads mentioned above.
Any other mods I did didn't really affect the bass as much. But the one biggest upgrade in bass I got was from pad rolling.
Edited by Mochan - 9/3/10 at 10:51pm