grizzlybeast
My name is grizzlybeast and I'm an audioholic.
That is not the consensus... though a lot of people prefer the 600, most with TOTL gear prefer the 650 also the 650 is said to be better technically. Someone I knew preferred the HD600 until they bought the Schiit Jotunheim and heard some of the 650's potential. They now use the 650.
Mass drop has done their research and Senn knows this as well which is why they chose the 650.
Hey, that sounds like me!
Anyone who bought a Jotunheim or is thinking about buying one owes it to themselves to buy a pair of these. The 650 was already the best value in the headphone world. If you plug it into a Vali 2, it sounds very good. If you plug it into a Jotunheim, it sounds great. If you plug it into an Eddie Current ZDS it sounds incredible.
At ~$350 it was already a deal given how much more expensive most top tier headphones are. At $200 everyone who loves audio owes it to themselves to try these. Even if they don't end up being your daily driver, these are reference cans. With some easy modding they're made even better.
Of course if you already own a 650 you don't need this.
That is you...
Here are some modding resources
https://www.youtube.com/watch?v=i9nL2M5-14g
http://www.head-fi.org/t/561234/sennheiser-hd-650-mod-compilation