Just a quickie. I wanted to ballpark the sound of these two separated-at-birth 'phones before launching into a pretentious, tendentious, adventitious and pernicious bunch of blather about the esoteric aspects of headphone listening, which I'm liable to do any time. Compared to the A-250, my refurb HD 600 sounds nocturnal, mellow, a little bottom heavy but pleasantly so, like a rich dark cup of syrupy french-roast coffee made in a Vietnamese press and drunk from a cobalt-blue cup. Highs go way up there but recede as they go up like the side of a skyscraper seen from ground level.
Well, I warned you.
Compared to the HD 600, the A-250 sounds very awake, alert, American; not quite bright but almost, dare I say it, old-school Sennheiserish. Bass is comparable but not as round, mellow and voluptuous. It's surprisingly good, a stinkin' deal at $44 shipped, but you already knew that.
There's nothing missing with either 'phone. The Senns are more like seductive aristocrats; they stand back. You're almost overhearing the hired help (in this case the Berlin Philharmonic) saw away at some Beethoven in the conservatory while you enjoy a glass of wine in the library. If you listen, you can hear everything, but it's at a discreet distance. With the Kosses you're whisked right up to a point just behind the conductor's scalp.
Having said all that (whew!), here's the kicker: they don't sound THAT much different. The Senns are basically flat and tilt up at the bass end, and the Koss, just as flat, simply tilt the other way.
Still breaking the Koss in, although I don't expect much more change in their sound. The Senns have been in daily use for months now here at The Lab (we found a sound card that'll drive them adequately) and can be considered well and truly broken in.
The Senns seem a couple of dB more efficient. Not much, and it's almost program-dependent.
So are the Koss the Retail Buy of the Year? It's starting to look that way, but it's early days yet.