I would stick with what you have. What you are saying regarding orthos smoothing things over is the opposite of my experience, as I would say orthos in general are very fast drivers and will capture details that dynamics miss. I should preface this by saying that I have never been a fan of the HD650s, feeling they do a very poor job of classical (large symphonic), I've never owned them however, but have heard them both single-ended and balanced on good amps (Dynahi, etc.) I haven't heard the HE500s, but have heard the LCD-2s (r1) in my own system and liked them alot.
+1 on reading your welcome PM (again).