Here are more detailed impressions. I'll go phone by phone, then amp by amp... not to compare apple to oranges, even though they were in different setups, but I believe a phone will keep its intricate character in every situation you put it into.
Hd650: I had never heard them, and had slightly mixed expectations about them, especially with two different cables and terminations. And the results were...... exactly what I had expected. The bass was precise and extremely textured, but it was not as tight and snappy as I would have liked. Even with the MPX3 on SE and with the apache in balanced mode, it had a noticeably bloomy character, and for a mid-head as me, it overpowered the rest of the music. I haven't tried it with my shanling, which has a slightly bright character to it with the stock tubes. Again, I definately didn't have the best experience with them, as they are 1000% open and I had to put it at much higher volume levels than what I'm used to, so take my impressions with a big grain of salt. But I still would have loved to hear the hd600 on the same setups.
Sr100: I liked the way these had a very balanced presentation overall, compared to the agressive upper midrange of my ATs and the sennheiser veil. However, no matter with what I listened to and with every setup, the midrange had a kind of brutish quality to it that made everything sound covered with a blanket. This was very noticeable when listening to movies. Again, I think the amplification was the problem, and that it would've needed much stronger amplification to shine on its own.
Sextets: I found those quite engaging and smooth, with very good midrange presentation. However, pushed by the little dot and the esound, it had very smoothed out transients and had some difficulty with dynamics, resulting in a sometimes boring experience. I could definately see myself living with them on a tight budget.
Denon D5000: I found them quite engaging for music with very little bass, as they seemed to give an extra oomph and texture to bass, but it overpowered the mids on most music to make it enjoyable for me. I think it would need very careful synergy when choosing the amp, source and even cables to bring it to its full potential.
more to come.