OK headphoners... I looked at the Grado RS-2s and while I think I would be in sonic nirvana, I see too many shortcomings for these to suit my needs. The biggest is comfort. In all my readings the size of the ear cups and the rigid foam seem to be long term listening hindrances. I'm certain I don't want to suffer comfort issues if I am spending $500-850 on a set of cans (the RS2e and RS2i respectively). Obviously they produce better than my other finalists with regards to midrange clarity and high end detail, really only lacking in depth compared to the Senns. I love their sensitivity and the super low impedance (32ohm) make them desirable as well. My headphone amp is perfectly capable of 32 ohm loads, and it handles my Senn Momentums easily. Now on to the Senns, which is really where I think I am going to end up... The question is, what do I gain by spending the extra $110 going from the HD600s to the HD650s? From what I can discern, the 650 is just more nicely appointed, using real metal cups and hardware, while the 600 uses plastic on the cups and as a cover for the band. While the 650s are listed at 10 Hz - 39.5 KHz and the 600s are listed at 12-39K, it seems they use the same drivers and architecture. They are both 300 ohm units (which is a bummer, but they are really efficient, and they will be driven with my tube amp), both are reviewed as beyond exceptionally comfortable, and they are really the only competitors to the RS-2 I feel I want to use. Finally, and I know I have beaten around the bush about this before, but I am going to ask a few questions directly... If I go full size on the Momentums I am moving into closed cups. Benefits: Bass responce and noise cancellation. How loud are the 600s and 650s externally? Obviously they will be audible, and I tend to listen to cans by myself, so it isn't a huge deal, but I don't want to be ridiculous at the same time. Also, is it really beneficial to have the cans so open and airy? I understand the benefits of a dipole, but I also understand the drawbacks... With a good dipole speaker you need a strong bottom end boost, so exactly how much does the dipole can suffer from bottom end losses? Or do I really need to shut the fuck up about the momentums and go with the open 600/650? Amp: I was bummed with the Mullard 6V6GT tubes. They really were nice and warm and had great depth, and they broke up really nicely, but the midrange was really muddy. Vocals were very distant. I have a set of Tung-Sol 6V6GTs in it right now. They are still breaking in, but everything is much more vibrant. So far I think I am a fan of the Tung-Sol (Russian made tubes). I am going to be trying a few other sets in the near future and will post about them if they are worthy.