The Sennheiser HD650 is a great pair of headphones. Makes a great complement to airier headphones.
Reviews by clams
DraconiaN
The HD650 which i also own have indeed a tendency to sound "dark" with a cheaper headphone amp...i've had the same sound issues with the stock JRC OpAmp ICs into my Xonar Essence STX Setup...after changing them to LME49720NA, it sounded clearly like a complete different headphone...much better in all ways, more crisp highs, mids...and not so strong bass, but i've found it well balanced, will give the LME49990 OpAmp a try...hopefully for the better sound experience. 
szoze
I don't agree these headphones have ability to give "great" texture to strings and woodwind. Those instruments sound in fact muted without higher harmonics and "bite". In my ears AKG K70x are much better in this department.
