I think you're hearing the same thickness or overlapping I speak of with the HD650s. The K701s in comparison are more airy and every performer on the recording sounds relaxed in their own space without overlapping, not one performer or detail is compromised. Again, I don't want to over-emphasize these differences - they are in reality subtle. One thing I'm certain of though is that my amp, the AGD Fun, has reached further into the K701s potential than it has the 650s.
A very interesting observation, sphinxvc, that the AGD Fun "reached further into the K701s potential than it has the 650s." I hadn't thought of it like that. Thanks.
I'm sure you're aware of the fact that you need more time to adjust and acclimate to a new sound signature. You're coming from the K701, so I can't say I'm too surprised with your initial reaction. I see you already know about the relative importance of burn-in. I'd give them approximately 100 hours (4 days) to open up (though changes will be audible much earlier).
I recall you confirming that you had suitable equipment to drive the Senns with. May I ask what specifically that gear is? This could be a synergy issue (warm, dark equipment with an already warm and dark pair of cans etc.).
Oh and yes, you're definitely spoiled by stats if that's what you're used to. But, I can't see how one would like the K701 and HD580 and not appreciate the HD650 for atleast its technical merit. The 650s are more revealing than both of the other cans so this could be an indication of the quality of the front-end. In any case, I anticipate a change in your opinion of the 650s in the next month or so. Keep us posted!
Thanks for the comments. Shahrose. My chain goes like this: Muse Model 10 CD/DVD-A player with balanced, variable analog output > Aesthetix Calypso, zero-feedback, balanced dual-mono tube preamp > Fiio E9 > the two headphones. (In-room listening system: BAT VK-120 mono tube amps and Pass Labs Aleph 60, single-ended Class-A solid-state mono amps; Quad 989 electrostatic speakers and two Vandersteen 2Wq subwoofers run as a stereo pair. I don't mean this as bragging, but you asked what sort of gear I was using.) I know some folks say the Fiio E9 is not adequate to pair with the 650s, while others argue ardently that it is exceptional (esp. for its price). Maybe it is a bottleneck in the system at present, maybe not.
The thing is, I had to get some kind of desktop amp to audition and burn-in headphones while I explored the head-fi world (remember, I am new to this side of the high-end hobby). I don't want to spend too much money until I figure out what my preferences are. Then I will be prepared to put larger expenditures in the right direction (e.g., HD 800, orthodynamics, or electrostats). I particularly don't want to spend too much on conventional amps yet, because it seems likely, with my sonic preferences, that I will ultimately go in the direction of Stax systems.
I appreciate your observations. As I indicated in my original post, I am not going to seriously evaluate the HD 650s until they have something like a solid week of burn-in. Some will think this wacky, but I had the K701 running around the clock for over a month before I really liked them without needing to add EQ.