Personally I am EXTREMELY SATISFIED with my setup:
Sennheiser HD650 +Cambridge Audio DACMAGIC and +GRAHAM SLEE SOLO SRG (Studio Reference Green) with its PSU1, connected via USB cable and ATLAS Equator MKII interconnect cables.
DAC MAGIC does a great job with iTunes compressed music but it adds little to my WAV files ripped using EAC and played with Foobar2000 software using ASIO Driver,
In both scenarios Sound is AMAZING, the headphones are really comfortable, open and accurate still warm enough...... if it's your first time you will spend hours and hours discovering details you never heard before in addition to unwanted sounds and noises in the background of the Studio or theatre where the recording took place
A Piece of Advice avoid importing electronics from overseas, because like everything these components might need servicing or may come defective so you will have to send them back for reparation, this happened with an eccentric Audiophile Friend of Mine who refused to buy a Graham SLEE like mine to drive his HD650 instead he went for an American Tube amplifier. Note that this Tube amp ranked N1 on a very respectable Audiophile website whereas my Graham SLEE Solo came in the 6 or 7th place , knowing that the number of amplifier reviewed was above 25 all of them costing more than 400£ and the result.... My Friend had to wait for 6 months for the boutique manufacturer to deliver and then what? One of the Tubes gave up after 24 hours of usage but the package included some spare tubes, however after 2 weeks we noticed a distortion in the left ear, till now we don't know if this is caused by the amplifier or the CD player., hope it's the later otherwise my friend will have to send back his 1000USD amplifier to the states.
By the way after buying my Graham SLEE and the HD650 I read an article stating that Sennheiser used Graham SLEE Solo amplifiers to demonstrate the high performance of what was then there flagship headphones and here I am talking about the wonderful HD650,
It is worth mentioning here that my favourite type of music is JAZZ, both instruments (i.e. Guitars, saxophone, cymbals) and human voices Sound Amazing through the HD650, Bass is tight and accurate and more than enough for my taste, I don't know about other headphones, but while Listening to one of Defected in the House tracks the Base was HUGE and precise even at deafening volume, in addition to my Jazz Library I rediscovered my PINK FLOYD, LED ZEPPELIN and WHITESNAKE CDs.
Hope that was helpful