I'm not much into headphone listening except when I edit audio ripped from CDs but I'm with Nick on this one.
I have a pair of Sony MDR-V6 for which I paid about $80. They are revealing enough to let me hear what I need to hear to make edits. I put $1K or more headphone amps squarely in the snake oil camp.
To make a transparent/linear headphone amplifier for most headphones, all that's needed is a $0.35 IC (JRC 4556), a low noise low power PS and a few capacitors and resistors that come in under $10-15 AT RETAIL PARTS PRICING. Add another couple of dollars for the crossfeed circuit, if you need that feature. Some headphones with abnormal requirements(extreme low sensitivity, need a bias voltage, etc.), of course, need a different solution.
I find the prospect of all of these expensive headphone amplifiers to be rather entertaining.
-Chris
