I liked the sound of the drivers, but if I moved my head a bit, or bent down to look at something (like maybe a mixing console), one or both of the earcups now become a bit looser, and pull away from my ears, not a lot, but just enough to change the sound. If I push a tiny bit on the earcups, exerting more force against my ears, the headphones sound much better. I did not keep these. Once again my SONY 7506's are still my reference headphone. I am about to try some Beyerdynamic DT-770 Pro-80 headphones. It'll be interesting to see how those compare to the SONY 7506's.  

If you're in the market for a high quality, reasonably priced, headphone amp, start with the Matrix M-Stage (and you may never need to go any farther). I recently (April 2014) visited the AXPONA audio expo in Chicago (what a great expo!), and auditioned numerous headphones, and headphone amps. One of my favorite headphone amps was the Woo Audio WA7 Firefly. But at around $1,000 it wasn't in my budget. Which brought me to the internet, in search of a stand alone, possibly Class A operation, headphone amp, with good reviews. Something that maybe sounded just as good, or close to, the Woo Audio Firefly, but at a lower price tag. I purchased the Matrix M-Stage, and love it to death. Let's face it, with audio gear, we all try to get as close to the music as possible (at least I do), be it in the studio, or a live performance. I am now much closer to the talent, when I listen to music on this headphone amp. Instruments and vocals just sound so clean, authentic, and close. Even though my current set of headphones are the SONY 7506, which have won my listening tests over and over, even with these headphones, it seems like the talent is right in the next room recording. This amp's noise floor (-95 dB) is super duper quiet too. Stereo tracking of channels is perfect. If you're comparing headphone amps, make sure you at least start with this one. It is worth every cent.