I respect your experience but using just one amp will not give you a proper insight into a headphones performance.
When I had the HD650's, with Silver Dragon cable, I did not have the system I have now but I managed to get a balanced HD650 to try last year in my current system.
It was the best I have ever heard them but they were still soundly beaten in most areas by all my other phones.
I have heard the Hd650's through a number of different systems now and although I enjoyed then when I had then, my standards are much higher now, they are just weak in too many areas.
The Senn amp is what works best with the 650's but I spent two years with the LCD 2.2's and then a year with the LCD3's and tried a wide variety of amps including balanced, solid state and tube. I finally figured out they just weren't going to happen for me.