With all sorts of equipment, the HD650 sound a bit different with each. And each seems to be an honest appraisal of the equipment. My SCD-XA777ES headphone out sounds a bit crisp and with a tipped up upper treble. With the Perreaux SXH1, it sounds fuller and more musical, and flat, but clearly solid state. With the WA6, it is seductive, and reveals different tube choices quite well, some being too warm in the midrange and rolled off, others being too extended on the extremes and "hi-fi."
|Either way, the 650 sounds to me a good bit more forward and 'etched' in the midrange than the 595, and not always as relaxed. I'd be interested to hear you expand on your post, especially on the 'enhanced midrange' comment.
I've never had that quality, not at all! Again, probably associated equipment. I find the midrange liquid and refined.
In any case, doesn't this sound like what you want in a headphone? Neutral, revealing, seductive.
By the way, my HD650 was out of warranty, but was replaced (one driver became weak) as if in warranty. Can't beat that.