Hey guys,
      So I just got my new pair of HD-555 and wanted to do everything right this time around.  So I will do my best to explain how to "widen" the soundstage for the Sennheiser HD-555/595 models.  Originally I used a soldering iron because that was the only thing in the how-to's other people created used.  I also ripped out the nylon baffle which I shouldn't have done.  So this time around, I will make it much easier, and better sound as well.  Stay tuned for my re-wiring of the HD555-595 because I will explain in depth how to do that.  Both of these mods can be done by a total novice like I still am.  They are pretty easy and you will definately get some better sounding headphones.  Beware that the soundstage mod is not reversible and both mods can void your warranty.  If you have any questions or want to give advice, please feel free to PM me.  Anyways, here goes for the HD-555/595 soundstage mod.
1.  Carefully peel off the earcup padding, they come off pretty easily, just don't rip it fast, do it slowly.  I found it's best if you reach your fingernails all the way to the inside and pry off.

2.  Next, you want to take off the outer most mesh grill.  This comes off just as easy, just use your fingernails or a flat-head screwdriver and reach in the little tabs.  Once you have one little tab up, just pry it underneath with your fingers and it comes off easily.

3.  Next, you want to take out the 3 really tiny screws.  Make sure you don't lose them!  Just place them in a safe place away from the headphones so the magnet doesn't pick them up!

4.  Now, carefully reach in the very edge of the earcup and pry it out, be careful here because the driver is attached to some very thin 32 AWG wiring.  Just pry it off a little, then set the driver next to the earcup and lay it flat.

5.  Now that the speaker is out you want to take the foam piece off to begin with.  Put this back in the box incase you want to use it for something else.

6.  Now that the foam piece is out, you can start prying up the grill tabs.  Be very careful here as well, because the tabs are pretty tiny and can snap off.  Also, there are like 2-3 tabs on each earcup that are hot glued in.  Just go behind the tab, scrape the glue out and pry it up.  Once you have them all pryed up, take your flat-head screwdriver and push down on a couple of them in opposite corners to get the grill off.

7.  Now, comes the fun part.  I say that sarcastically.  Now get some tiny scissors like sewing or nail scissors and start poking them through the tiny holes of the inside.  I found that using 2x1 length's work the best, refer to the photos for that.  I made mine perfectly round so I wouldn't get any distortion, plus i'm a perfectionist, but you don't have to if you don't want to.  If you do want to, just get a blade and go around the outer wall on the inside.  Just be very careful when doing this.  Make sure you watch out for the screw holes, there are 2 on each cup that should stay there and you will go around them.  Don't try to shave it from the outside, because I accidentally scraped through on one part.  Nothing some epoxy can't clean up.  I actually just thought of something, if your going to make it perfect like I did, I would just do it with the blade instead of using the scrissors at all.  This way, you get much more to work with and it will come out nicer if you want to put it back in.  I guess you really do learn something new every day.


8.  Once you got that inner grill piece out, the hard work is over with.  Now, all you gotta do is put everything back in reverse order.  Make sure the speaker driver is facing the same way and be careful with them wires.  Just put your driver back in, the screws back in, clip the outer mesh grill in, and clip the outer ear cushion in.  Like I said, it's easier than it looks I would say.  Stay tuned for my re-cabling of the entire headphone!
And here are photos of the before and after look.