I wouldn't like to pay awful lot more than a pair of HD 650's. I really can't spend thousands for a pair. Was kinda balancing AKG and HiFiman in my mind.
I've been looking at those actually. The only problem seems to be the European pricing, making the headphones cost 200€ more than a pair of HD 650's. This is thanks to someone thinking €=$, which would make HE-400i cost $632 and the HD 650's cost $375.
Oh okay. Maybe AKG Q701s or the Beyerdynamic DT880--both classic midfi cans--would be more suitable. They definitely complement, rather than totally compete with, the HD-650s slightly darker, warmer, and smoother sound signature. I like having headphones with different signatures because, like having different colored glasses, I perceive the same object from a different perspective.
The HE-400i also sounds very suitable.
+1 I have both the Q701 and DT880 600 ohms.