Well based on this post I jumped on a pair of Sennheiser HD650 headphones and it has been quite the adventure. I got lucky and got the headphones below $299 a little after when this was posted.
It took me forever to get the sound dialed into my liking and hear the awesomeness from these headphones. This is the short of it.
1st there was the break in which took about 2.5 weeks. I found the sound was still lacking so I then jumped on the upgrade cable specifically for these headphones from Furutech. The sound still improved but was still sounding eh from my solid state headphone amp. Through some reading I found OTL headphone amps can make these headphones sing. I was able to secure an Antique Sound Lab OTL headphone amp but bass was too boomy. I was at a Guitar Center and bought the Groove Tubes EL84 tubes from Slovakia with normal distortion. Those tubes combined with a Raytheon 12AX7 NOS tube gave me music heaven. I'm not changing now.
If you score the Sennheiser HD 650s be patient. Getting them to sound good in your rig can take a bit. I'm happy I stuck through it.