Well I'm not sure if the D600 will be for me or not...but in that same price-range I can get into Orthos via modded F50RP's.
I'm torn between the Mad Dog's for $299 w/alpha pads: https://www.mrspeakers.com/MrSpeakers-Mad-Dog-Alpha-Pad-Fostex-T50RP-headphone
Lot's of love and reviews here...I have been told not to expect D2000 bass then some say it's so much better. I am a bass head but I appreciate good, fluid, bass. It doesn't need to rattle my brains but when I want lots of it I want it on demand. I have read more than a few times that these are claimed to be the best closed headphone for under $300-500.
Next, I found mayflour electornics V3... which they told me if I wanted skull shaking bass was my best choice, in their lineup. https://www.mayflowerelectronics.com/store/p12/Fostex_T50RP_-_Version_3.html
Without them gluing the SRH-840 pads on, and ordering some Alpha Pads (fwir this is worth it), they'll be the same price as the mad dogs.
Anyone have experience with both? Either? vs. D2000? There's a great review of the Mad Dogs and gaming, especially with Borderlands 2. I love that game! And BF series, right now I'm playing X3 and Evochron Mercenary.