The "new version" of the HD650's, "de-veiled, with a silver cable... and... a high impedence, high voltage amp, which has enough power to drive them properly... are... about as good as it gets - very comparable to any of the so-called "high-end" phones. Configured in that manner, they sound a lot like the better Grados, or the AD2000's - which is superb!
So... IF... you plan to configure them in that manner - you will be very pleased... and... know there is not anything that is much better. I've compared them to most, and can attest to that.
IF NOT... then... you need to get some other phones that don't require all of that to sound their best. Those would be Grados, ATH-AD2000's, Denon D-5000's / 7000's (with the Markl Mods), etc.
Now... you can search for the HD650 threads for the complete explanation of all of that.