Ok so I'am curious to try this mod, but this member isn't active for quite a long time, so I can't PM him...I have been listening to the 600's quite a bit, however, I still find the bass a bit overbearing. So like any good Headfier I decided to open them up and have look and see if there was anything I could do to tame the bass. Once inside my suspicions were confirmed as there are two open holes on the back of each driver. I decided to cover one of them up with double sided tape. It was better than stock, a lot less bleed into the midrange and much less sloppy and overbearing. So I thought if covering one was good then covering both would be even better. So I covered up both holes, put everything back together and had a listen. Nope. Too much of a good thing. Covering both holes killed a lot of the bass, took away a lot of the fun factor of these phones. I liked them better with only one hole covered. I removed the tape from one of the holes and confirmed what I had originally thought, one hole is the best. Bass is much punchier, less bloated and sloppy.