I don't have a HD600 to compare it to, I'll get one though if you want - the more the merrier. I do have a HD598 on my desk right now. The M-100 is semi-closed as all of our models thus far. I appreciate open-back's qualities, but I just love the isolation, immersion, "vivid" mids and staging psychoacoustics of semi-closed.
Agreed, I also love semi-closed designs. However I didn't hear much of the improved soundstage in LP2 though. If I wouldn't be selling it I'd gladly try removing the foam cover at the back of the "V3 port" to improve the air flow and possibly mask one or two of the 3 holes if needed (well try out exactly how much should be left open once the foam is removed). By completely removing the foam of any vents usually results in even better soundstage and bass response with somewhat increased natural treble but it's all down to how much is left completely open and can be ofc tuned. Ofc isolation is slightly worsened but I'm more interested in sound quality. :P
But have you tried perhaps playing around with the foam that's there to something else that might let better airflow through?
Edited by RPGWiZaRD - 2/4/12 at 1:51am