I've never heard the 595s but they must be some really dull sounding phones to make the 650s sound unforgiving and harsh. I guess everything is relative...
"Here is the shocker - the HD-650 has more treble detail/resolution and actually sounds brighter in my setup. The 595 has a hollow tonal balance in the treble compared with the HD-650. Now this is a shock to me because my initial impressions were that the 595's were too bright!! It is consistently brighter than the HD-650 but the real "bright spots" of the music (Cymbals, Snare, guitar) are brighter on the HD-650."
This was exactly the point I was trying to make, not that the 650 was "brighter" in the sense of having more treble (the 595 has more), but that it has a slightly forward, "bright" midrange that gives greater resolution but at the same time can sound harsh on strings and give recordings with too much reverb a cave-like sound. There's more than one definition of "bright", and I obviously was not able to convey adequately the one I meant.