[LTSFBH]

Found this simple and inexpensive mod recently, during a recent trip around the interwebs. I don't remember the site, but will post an update once I find it, to give the author credit. The author was a big fan of Grado headphones. At the time he wrote his article, the PS500 was his favorite. His only gripe was the comfort issue. Like him, I find the comfort lacking and have trouble wearing them for extensive listening sessions, which is a problem since I've been listening to a lot of Phish lately! This mod, named after it's resemblance to a sunflower (Or maybe a bumble bee?), is simple, inexpensive, quick, easily reversible and in my opinion has no appreciable effect on the sound signature, other than maybe a bit deeper bass.
 
Simply take a Sennheiser HD414 pad and cut about 1/4" off the edge. You can do a neater job than I did, but it will be completely hidden so no worries.
 

 
Put the trimmed pad on your chosen Grados and then replace the original pad.
 

 
I personally think it looks good. The comfort is increased tremendously and so far I like the way it sounds. Just got an 8 disc Phish compilation, so I'll know for sure later tonight!
 
PS This was done on my SR325e's. I am going to try it on my PS500e's as well.

 

[Pingupenguins]

This could also help with debris on the driver. I've seen a lot of that on the grado headphones which can attribute to buzzing. Not sure how acoustically transparent that is though. I feel like the foam in front of the driver could cut out the treble that Grado's are famous for. 

 

[LTSFBH]

I suppose you could always quarter mod the Senn pads if that seemed to be the case for anyone. I think you would still get the comfory benefit. I personally can't listen to the SR60,80 or 125 for too long. I find them too bright and this might be a good mod if I still had any of those. I've moved on to the 325e and PS500e and have no complaints on the sound signature with this mod.