Just want to chime in on the AH-D600 that you can power it fine without an amp. It needs a good source but was designed to be directly used out of portables. As an over ear closed back, it so comfortable. Though it does seem to be design for those with medium-to-large noggins. I have fairly large ears, and they fit fine inside of the shaped cups. Its very enjoyable listening to cinematic music, movie scores, thanks to its rich bass. Its a headphone that had its hare of criticism, but I really enjoy it - its quite relaxed, and I just seem to gel with it and want to listen hours on end.
The great thing about it, well they've been going for good prices, way below the MSRP.
I've owned the MDR-V6, its been a while but I remember it as an excellent headphone. Especially for its price. The high-end could get a bit sharp.
Oh, another recommendation would be the Shure SRH-840 and SRH-1540. Definitely read up on the latter. Its fairly new and has been described as a mixture of AH-D600 meets Sennheiser HD650. I've owned the SRH-840, and I prefer the Denon AH-D600, more for the better soundstage, clarity, and low-end. The SRH-840 is more a monitoring headphone in the vein of the MDR-V6. Some may prefer that type of sound. The SRH-1540 is more tuned for musicality and enjoyment.
Also would look into the MDR-7520. A proper studio can, but one that is said to have incredible bass reproduction while remaining neutral, also very comfortable.
Just listening to some tracks from Two Steps from Hell, Audiomachine, and they are using modern production techniques and effects processing, including drum sampling and synthetic percussion. On the D600, you'll definitely get the impact from the percussion and lower bass they've worked into tracks.
+1 to this. The Denon AH-D600 also offer deeper, and more bass than the SRH-840. Speed wise, the AH-D600 did ted better IMO