They leak. Which is natural for an open can. But for me it is a non issue.I wouldn't use these in the library or an office, but outdoors walking around or doing yard work. Nothing like having that large stage to make you enjoy yard work. I have my iems ,MA750s if I want isolation..They leak a little less than the AD900X but they do leak sound out. They do a great job blocking sound coming in though with music playing. I trust Dannys view of them CAL2s. If you want one with less leakage I would snag one of them. You already own the HA-S500. I think them HA-S680s have potential but them CAL2s look way more comfy and I bet they sound great too.. I was very close to getting them CAL2s myself but I read a review from another member that they have a very similar sound to the original CALs which is not a bad thing but with better refinement..They could be using the same exact driver but better tweeked and obviously better larger housing for the drivers.
Oh yea I forgot I briefly tried one of my games using the Yamas . Call of Juaresz Gunslinger...A western shooter.. These Yamas sound as good if not better than anything I have ever used for gaming. Perfect sound positioning and gun impact..
Sure, sound leakage is a concern, but it's definitely less important than the sound itself. The main thing that I have a problem with is the lack of imaging with the AD900X. The bass could be a little better as well. I'm tempted to buy these Yamahas just to see if I really do like closed cans better. I haven't even considered the CALs. Well, you know me. My favorite sound signature is that of the CKN70s and the Gratitudes: warm and bright. My primary concerns are imaging, instrument seperation, and sound stage in that order. The CAL2s are a little tempting because of the inline microphone and portability.
Honestly, I'm still curious about the WS99s. They seem like they would have a similar signature to my beloved Gratitudes. But at the moment you've got me eyeballing the Yamahas with my debit card out.