I know they are already up on the list, but definitely the HD600 and HD650. If you can find either of them in the $275-350 range, I think they're a steal relative to most other headphones. Competitive with some of the supposedly "better" or, at least, more expensive headphones on the market. I've never found a perfect headphone. So, they're not perfect, but they do seem to do more right in general and less wrong than many other better and/or more expensive headphones.

Stock, both have a noticeable emphasis centered around 100Hz. Coupled with some slightly high harmonic distortion in the bass, more so on the HD600, you get a slightly muddy or slow sounding headphone when compared to the best. The HD600 to me was a bit hot in the 1-4KHz range and could use extra treble smoothness. The HD650 is smoother up top, especially in that 1-4KHz range, but might be a bit too recessed and laid-back in spots. In the end, these are pretty minor complaints compared to many other headphones. Regardless, they offer a very enjoyable sound stock and, as I've read, scale very well.

Now, based on my experiments and subjective impressions, stick some damping in the back of the cups, and maybe some in the front, and that goes a long way in cleaning up the HD600/650's bass and overall sound. More cohesive. Cleaner. Put some damping in front if you need even smoother upper-mids and treble. Stretch them out if the clamp is too hard, which should also improve the treble response.

I bought these and realized I should have stopped dancing around the Senns for years. Always had some excuse to not buy them and try something else. These should have been my first "high-end" headphone purchase. That's why I'd nominate them.

Hans, do you have pics of the dampening inside? I saw the links you posted in the HD650 measurements thread but I can't recall any photos. I'd like to give it a try on the 580's!

I definitely like to experiment a bit, just trying to figure out where you put it. I guess it's been a while since I've taken my grills off...

Update your firmware. It's a whole different beast now.

Many of us were using it solely as a DAC previously to other amps as well.

Too late . I borrowed the Geek Out a few days , tried it once. heard my IEM (SE535) as loud as little speakers on my desk . After that, I settled the volume, heard the noise and send the Geek Out back immediately.