I know what you mean. Its very rare for headphones to be able to deliver the sort of sonics that the HD650 is capable of. I have recently balanced my stock cable and using the Audio GD Phoenix...the HD650 can scale to have a massive soundstage and pinsharp imaging with very good speed!
That scalability is what keeps the 650 as one of my favorite headphones, it makes them a proposition of great value. It is one of those cans that can convince you that amps do make a difference, now I don't know if there is something inherently better in having them balanced, but a balanced 650 with say a beta22 is a very very good rig.
I think they are in a tier behind the SOTA right now (HD800, LCD-2, etc), but in no way they are mid-fi like I have read in other threads lately. I think that may be because since they are now a lot cheaper than the average flagship, people use them in less than ideal situations (which doesn't necessarily require huge amounts of money, but some time to research what goes well with them) and don't hear their full potential.
I feel like a lone voice trying to convey this to others on this forum. Simply stating this view will have you pegged as a shill for expensive gear when all you are trying to get across is how revealing the HD650 is, and any deficiencies in your chain will be shown without remorse.
It's fine to prefer the exaggerated bass and treble presentation found in other cans but to pigeon hole the HD650 as slow, boring and veiled simply highlights how far one is from glimpsing the HD650's potential. It's a real shame actually, because this view then gets perpetuated by even less knowledgeable members (apparently first hand experience isn't required anymore before commenting on such a hotly debated topic) and the HD650 is brought to the gutter as laid back or boring.
I just don't understand how these people can claim those qualities are inherent in the HD650 when they're not to be found on my headphone through my setup. I refuse to believe an amp and dac could be good enough to lift an inherently slow and boring headphone to one that's lush, engaging and authoritative. To me it seems logical if the headphone itself was technically capable in the first place, but that it requires the right components to truly shine.