Ssutherland, when I use my Senn 650s with my HK, I turn the volume somewhere between 30-25. They like a lot of power. Normal listening levels with speakers finds the volume at 40. To me, the Senns feel kind of flat with the receiver headphone output and I catch myself upping the volume to dangerous levels trying to attain some kind of dynamic response. I've read that some receivers don't put much into the power supply part of the headphone output. I don't know if this is technically true or not. On an interesting note, I have a tube preamp which is supposed to have a beefier headphone section. All I know is that I don't have to turn the volume way up when I listen to the Senns. I'm thinking the preamp does offer more power, and the sound is very dynamic to my ears.
Again, I don't know the techinical aspects of it, just giving you my thoughts.
