Everyone should remember that your headphone experience will *never* match the FR graph. Not only is the graph generated using a test head with mics in ear canals that aren't shaped like yours (and probably cause the big spikes and dips that always seem to be near 4 or 8 KHz on almost all phones, odd huh?), but also your amps will have different output impedance from the test amp.

In most test systems I've worked with, the source impedance is usually less than 1 ohm, often a lot less. If you have a receiver, you might have 300 ohm output impedance, which will cause a signifant (as in 1-3 db) increase in bass as well as bumps in other areas of the frequency spectrum.

I post this a lot on head fi because many people don't understand that there is a mathematical relationship between the ratio of amp output impedance to headphone impedance, and unless you have an ortho with a very flat impedance curve, the ratio of output impedance to headphone impedance has a real effect on sound...

Happy reading for the curious (it's an easy read, and informative)...

http://www.avguide.com/blog/why-headphone-amps-sound-different-frequency-responseimpedance-issues