John, I love to hear your impression between the SR71a and SR71B. I sold my SR71a after I received my 71b. To me, the 71b is much more dynamic, more air, more open with bigger soundstage, more personal, more PRat, better bass, it is just more fun and more life like than the 71a. I am not trashing the 71a at all. It is a great amp, but it is sort of boring for me. It is there and does it job with almost any phone you connect to it. I was having the 71a and the Mustang for almost a year and I preferred the Mustang over the 71a for some of the above reasons when I use my JH13. But one thing for sure, if using full size cans, the 71a did better than my Mustang.