After checking Head-Fi I see that I probably don't have a good match between my headphone amp. and cans. I've got a Headroom Headphone Total Bithead mobile Amp., 2.66 MacPro, and Sennheiser HD650's (that are hard to drive). The amp. has a high and low gain switch. The low gain sounds better, but I can't get enough vol. when on low gain. I've got iTunes level up as high as it can go. I've played around with Sound prefs. and the Audio/Midi sound levels. They all seem to actually be the same vol. control. I also see that iTunes, under "Get Info" has an individual vol. adjustment, but I'm not sure if I really want the sound files to be pumped up for when I use them on my iPhone. Is there any other output control that I could tweak the vol. up so I could use the low gain setting. If not I guess I've got to RMA this and get the next amp. up the line. The Headroom Total Bithead sounds great with my Audio-Technica Quiet Points by the way. Of course they are pretty efficient compared to the Senns.